jpeg: Consolidate error handling

Make all error paths in gdk_pixbuf__jpeg_image_load
go through the same path, so we don't forget to free
the exif data in half of them.
jpeg: apply icc profile when loading incrementally

This was apparently never tested, and thus didn't work.
Add a test for icc profile loading

This test verifies that the preceding commit indeed
makes icc-profile loading from jpeg files work.
Fix another potential leak in an error path

If we longjump out of libjpeg, we may have already parsed
the exif data, so free that as well.
2.30.2
Bump version
build: Use UNIX Line Feeds for MSVC Projects

... so that it would be more consistent with the rest of the source files,
and application of patches would be easier and cleaner.  The README.txt and
.sln files under build/win32/vs* still has to have DOS/Windows line feeds.
Unify sniff buffer size

GdkPixbufLoader was using 1k as a buffer size for sniffing file types,
and the gdk_pixbuf_new_from_file() family of functions was using 4k,
for no good reason. Unify this so we use the same buffer size
everywhere.
More sniff buffer size unification

Turns out gdk_pixbuf_animation_new_from_file() was also
using a different size.
Refactor things a bit

Move the generic incremental loading into its own function
so we don't end up taking two 64k buffers on the stack when
one is enough.
Some more stack conservation

Only use the sniff buffer while we need it.