Support for content-type when serving blobs in raw mode

[vgheo]

Use case :
A git repositiory is used to store static web contents (html, xhtml, xml+xsl).
Files contain links with relative paths within the same tree.
When the repo is browsed in gitlist at any commit:

• a) the 'raw' URLs for html / xhtml/ xml+xsl files shall be properly presented by the browser
• b) the relative links in the files shall resolve to respective files in the same commit

Currently all files in raw mode are served as text/plain, which prevents the desired behaviour.

Note that gitweb does generate proper mime types in raw mode. However, due to the URL structure, gitweb cannot support requirement b) above.

I have experimented by changing the gitlist BlobController.php to serve only text/xml, and results are positive. (see patch).

[alehaa]

Seems to be related to #451 and #452.