Because Haml automatically indents the HTML source code, the contents
of whitespace-sensitive tags like pre and textarea can get screwed up.

Simply type a name with a `/` directory separator and new directories
will be created. This does not do the fancy UI work that github.com
does, but it will get the job done.

I could not find tests for file creation, so I didn't add a test for
this slight behaviour modification. I did test directory traversals
though, using both absolute paths like `/tmp/foo.txt` and relative paths
like `../../foo.txt`. Neither case escaped the repository, though
attempting to traverse with a relative path resulted in a 500 error that
did not affect application stability upon reload.

Closes https://github.com/gitlabhq/gitlabhq/issues/8763

Change "+" icon under "Files" section to have three options:

* Create file
* Upload file
* New directory

Upload file is no longer accessible from the "Create file" page.
Users can now select a target branch in upload file as well.

Closes #2799: Fixes a bug where file modes were overwritten after a commit

Closes https://github.com/gitlabhq/gitlabhq/issues/8253: Existing files
can no longer be overwritten in the "Create file" section.

Closes #2557

Dynamically adjust placedholder for uploads and fix Dropzone event handlers

Override error handler to prevent error messages from being inserted underneath image preview

Fix tests

Use regexp instead of startsWith for better browser compatibility

Remove duplicate code in _replace.html.haml and use one template

Remove files upon error and retain alert messages until user adds a new file