Allow buffer local mappings to overwrite existing mappings.

If the fileype is vimwiki then the vimwiki mappings take precedence.
Global mappings will not be overwritten. Closes #699

autoload/vimwiki/u.vim

@@ -76,24 +76,20 @@ endif
 " a:1 optional argument with the following functionality:
 "   if a:1==1 then the hasmapto(<Plug>) check is skipped.
 "     this can be used to map different keys to the same <Plug> definition
-"   if a:1==2 then the mapping is not <buffer> specific
+"   if a:1==2 then the mapping is not <buffer> specific i.e. it is global
-" This function maps a key sequence to a <Plug> command using the arguments
-" described above. If there is already a mapping to the <Plug> command or
-" the assigned keys are already mapped then nothing is done.
 function vimwiki#u#map_key(mode, key, plug, ...)
   if a:0 && a:1 == 2
-    let l:bo = ''
+    " global mappings
-  else
-    let l:bo = '<buffer> '
-  endif
-
-  if a:0 && a:1 == 1
-    if maparg(a:key, a:mode) ==# ''
-      exe a:mode . 'map ' . l:bo . a:key . ' ' . a:plug
-    endif
-  else
     if !hasmapto(a:plug) && maparg(a:key, a:mode) ==# ''
-      exe a:mode . 'map ' . l:bo . a:key . ' ' . a:plug
+      exe a:mode . 'map ' . a:key . ' ' . a:plug
+    endif
+  elseif a:0 && a:1 == 1
+      " vimwiki buffer mappings, repeat mapping to the same <Plug> definition
+      exe a:mode . 'map <buffer> ' . a:key . ' ' . a:plug
+  else
+    " vimwiki buffer mappings
+    if !hasmapto(a:plug)
+      exe a:mode . 'map <buffer> ' . a:key . ' ' . a:plug
     endif
   endif
 endfunction

ftplugin/vimwiki.vim

@@ -487,20 +487,20 @@ if str2nr(vimwiki#vars#get_global('key_mappings').lists)
 
   " change symbol for bulleted lists
   for s:char in vimwiki#vars#get_syntaxlocal('bullet_types')
-    if !hasmapto(':VimwikiChangeSymbolTo '.s:char.'<CR>') && maparg('gl'.s:char, 'n') ==# ''
+    if !hasmapto(':VimwikiChangeSymbolTo '.s:char.'<CR>')
       exe 'noremap <silent><buffer> gl'.s:char.' :VimwikiChangeSymbolTo '.s:char.'<CR>'
     endif
-    if !hasmapto(':VimwikiChangeSymbolInListTo '.s:char.'<CR>') && maparg('gL'.s:char, 'n') ==# ''
+    if !hasmapto(':VimwikiChangeSymbolInListTo '.s:char.'<CR>')
       exe 'noremap <silent><buffer> gL'.s:char.' :VimwikiChangeSymbolInListTo '.s:char.'<CR>'
     endif
   endfor
 
   " change symbol for numbered lists
   for s:typ in vimwiki#vars#get_syntaxlocal('number_types')
-    if !hasmapto(':VimwikiChangeSymbolTo '.s:typ.'<CR>') && maparg('gl'.s:typ, 'n') ==# ''
+    if !hasmapto(':VimwikiChangeSymbolTo '.s:typ.'<CR>')
       exe 'noremap <silent><buffer> gl'.s:typ[0].' :VimwikiChangeSymbolTo '.s:typ.'<CR>'
     endif
-    if !hasmapto(':VimwikiChangeSymbolInListTo '.s:typ.'<CR>') && maparg('gL'.s:typ, 'n') ==# ''
+    if !hasmapto(':VimwikiChangeSymbolInListTo '.s:typ.'<CR>')
       exe 'noremap <silent><buffer> gL'.s:typ[0].' :VimwikiChangeSymbolInListTo '.s:typ.'<CR>'
     endif
   endfor
@@ -510,19 +510,15 @@ if str2nr(vimwiki#vars#get_global('key_mappings').lists)
     " Valid only if langmap is a comma separated pairs of chars
     let s:l_o = matchstr(&langmap, '\C,\zs.\zeo,')
     if s:l_o
-      if maparg(s:l_o, 'n') ==# ''
       exe 'nnoremap <silent><buffer> '.s:l_o.' :call vimwiki#lst#kbd_o()<CR>a'
     endif
-    endif
 
     let s:l_O = matchstr(&langmap, '\C,\zs.\zeO,')
     if s:l_O
-      if maparg(s:l_O, 'n') ==# ''
       exe 'nnoremap <silent><buffer> '.s:l_O.' :call vimwiki#lst#kbd_O()<CR>a'
     endif
   endif
 endif
-endif
 
 function! s:CR(normal, just_mrkr)
   if vimwiki#vars#get_global('table_mappings')
@@ -538,13 +534,9 @@ endfunction
 
 " insert mode table mappings
 if str2nr(vimwiki#vars#get_global('key_mappings').table_mappings)
-  if maparg('<Tab>', 'i') ==# ''
   inoremap <expr><buffer> <Tab> vimwiki#tbl#kbd_tab()
-  endif
-  if maparg('<S-Tab>', 'i') ==# ''
   inoremap <expr><buffer> <S-Tab> vimwiki#tbl#kbd_shift_tab()
 endif
-endif
 
 " <Plug> table formatting definitions
 nnoremap <silent><buffer> <Plug>VimwikiTableAlignQ