Keep a tab inside a BTags pattern from cutting the address

ctags leaves a tab as it found it, so splitting the source line on tabs left
'/^' for a tab-indented definition, which matched whatever line came next, and
'/^static int g = 1;' for a tab later on, which only happened to match. Write
the tab as '\t', which matches the same text and keeps the address one field.

:BTags with 'ctags --excmd=pattern' now reaches every tag in a tab-indented
file, where the address was a fragment before.

autoload/fzf/vim.vim

@@ -1653,6 +1653,14 @@ endfunction
 " ------------------------------------------------------------------
 " BTags
 " ------------------------------------------------------------------
+" ctags leaves a tab inside a pattern as it found it, and splitting the line on
+" tabs would cut the address short, leaving a fragment that matches some other
+" line. '\t' matches the same text and keeps the field the line's third
+function! s:tabs_in_address(line)
+  return substitute(a:line, '^\%([^\t]*\t\)\{2}\zs.\{-}\ze\%(;"\t\|$\)',
+        \ '\=substitute(submatch(0), "\t", ''\\t'', "g")', '')
+endfunction
+
 function! s:btags_source(tag_cmds)
   if !filereadable(expand('%'))
     throw 'Save the file first'
@@ -1669,7 +1677,8 @@ function! s:btags_source(tag_cmds)
   elseif empty(lines)
     throw 'No tags found'
   endif
-  return map(s:align_lists(map(lines, 'split(v:val, "\t")')), 'join(v:val, "\t")')
+  return map(s:align_lists(map(map(lines, 's:tabs_in_address(v:val)'),
+        \ 'split(v:val, "\t")')), 'join(v:val, "\t")')
 endfunction
 
 " Position to return to with CTRL-T. Captured before fzf opens, because the