Adds 'image/x-ms-bmp' as an allowed mimetype for images, and is
equivalent to 'image/bmp'.  The image module is also updated to expect
this new type.

I found an image of mine that, when uploaded, PHP thought was
'image/bmp', so it was allowed.  However, when cropping, PHP though it
was 'image/x-ms-bmp' and failed to lookup a loading/writing function.

Signed-off-by: Malf Furious <m@lfurio.us>

Adds 'image/bmp' as an allowed mimetype for images.  The image module is
also updated to expect this new type.

Signed-off-by: Malf Furious <m@lfurio.us>

Adds 'image/gif' as an allowed mimetype for images.  The image module is
also updated to expect this new type.  For background images, animated
gifs will work properly.  For head images, the cropping process
truncates the image to only one frame; this is probably for the best.

Signed-off-by: Malf Furious <m@lfurio.us>

User-supplied head images will need to be square in their dimensions, so
that bootstrap displays them correctly.  This function will crop image
files after they are uploaded to the server.