Part of the reported issue was previuosly fixed by dc497ed0 (smaller size images being blanked).
This commit fixes the remaining bug with original-size avatars being left as BMP (which could include the 96px size for instance, which could cause problems in browsers not supporting BMP natively)
Added ImageFile::copyTo() as a convenient alias for resizeTo() when not resizing; this performs the BMP/XPM/XBM->PNG conversion if needed, or copies the original file.
Copying instead of using move_uploaded_file() is fine here since:
a) the files are cleaned up on script completion anyway (vs moving to remove it)
b) we're already performing getimagesize() and possibly load/resize on the file before this point (vs needing to move the file into a usable area to work with open_basedir restrictions that prevent working directly with uploaded files in the temp dir; since this would fail anyway, we lose nothing)
ImageFile::preferredType() now works on $this->type instead of asking for one, to make it handier to use from outside. (This is still needed in order for calling code to generate a target filename.)
Recommended for future:
* additional consolidation between the various ways of uploading avatars (touched avatarsettings, grouplogo, and apiaccountupdateprofileimage with similar minor changes)
* consolidate type checks and file naming into Avatar class
Moved the common_avatar_* functions to the Avatar class. Typically
either as methods on the object or as static methods. Replaced all the
uses of the functions in other modules.
