Add mime.type for .m4v files

[www.google.com/accounts/o8/id?id=AItOawledtwJVR8tIu1Dq-KLW1tTypIFgPHaf4o]

.m4v files are Apple's version of MPEG4 and according to ​http://en.wikipedia.org/wiki/M4V their mime.type is video/x-m4v

They can be used with Flash-based players and lack of proper Content-type header creates issues in (at least) Firefox.

Attached is the trivial patch.

[www.google.com/accounts/o8/id?id=AItOawledtwJVR8tIu1Dq-KLW1tTypIFgPHaf4o]

Add video/x-m4v mime.type for .m4v extension

[is]

In [4232/nginx]:

Adding m4a and m4v MIME types (closed #42).

[is]

In [4252/nginx]:

Merging r4190, r4232:

MP4 related fixes:

*) Fixing mp4 module seeking on 32-bit platforms.

*) Adding m4a and m4v MIME types (ticket #42).