Handle filenames containing equals signs.

autoload/gitgutter/sign.vim

@@ -77,7 +77,7 @@ function! gitgutter#sign#find_current_signs()
     silent execute "sign place buffer=" . bufnr
   redir END
 
-  for sign_line in filter(split(signs, '\n'), 'v:val =~# "="')
+  for sign_line in filter(split(signs, '\n')[2:], 'v:val =~# "="')
     " Typical sign line:  line=88 id=1234 name=GitGutterLineAdded
     " We assume splitting is faster than a regexp.
     let components  = split(sign_line)

test/filenameWithEquals.expected

@@ -0,0 +1,5 @@
+
+--- Signs ---
+Signs for =fixture=.txt:
+    line=1  id=3000  name=GitGutterLineAdded
+    line=2  id=3001  name=GitGutterLineAdded

test/testFilenameWithEquals.vim

@@ -0,0 +1,12 @@
+source helper.vim
+
+edit =fixture=.txt
+normal ggo*
+try
+  write
+  write
+  call DumpSigns('filenameWithEquals')
+finally
+  call system('git reset HEAD =fixture=.txt')
+  call system('git checkout =fixture=.txt')
+endtry