create new undo block for formatting (fix rhysd#30) (rhysd#55)

* create new undo block for formatting (fix rhysd#30)

This creates a new undo block to only contain the changes introduced by
clang format but still preserves the original cursor position.

* fix creation of undo block in visual mode at line 1

* redirect yanked text to black hole register

* suppress autocmd events when creating new undo block

Author: 0xC0FFEE

autoload/clang_format.vim

@@ -232,6 +232,11 @@ function! clang_format#replace(line1, line2)
                     throw 'fallback'
                 endif
 
+                " Create a new undo block to separate all formatting related
+                " changes from the last undo block but still preserve original
+                " cursor position (issue #30).
+                silent execute "noautocmd normal! ii\<esc>\"_x"
+
                 call setreg('g', formatted[i+1:], 'V')
                 undojoin | silent normal! 2gg"_dG
                 silent put g