[cairo] Assorted patches to fix warnings

[Pavel Roskin]

Hello!

While debugging Evolution on x86_64, I encountered a bug that looked
like to be in Cairo.  It turned out that Cairo was dealing with memory
corrupted elsewhere.  Nevertheless, I decided to perform some formal
checks on Cairo to make sure that the foundations are solid.  It looks
like they are.

However, I had to make many fixes to reduce the number of warnings or to
simplify some checks.  Trivial as they are, those fixes won't fix any
bugs in Cairo.  But they remove lots of annoyances for those who will
also use formal checkers and thus encourage their use.

Actually, I think _FbOnes() could become faster on 64-bit systems
because it counts bits on a 32-bit integer now rather than on a 64-bit
long.

Somebody should check if _CAIRO_FORMAT_TO_XRENDER_FORMAT() should be
handling CAIRO_FORMAT_RGB16_565 the way it does (implicitly before the
patch and now explicitly).

I also wonder if ps_standard_encoding in src/cairo-type1-subset.c is
supposed to correspond to ISO-8859-1 encoding.  If so, it needs to be
seriously rearranged.  The indices in the comments were wrong starting
at 160.

I'm going to send all the patches using "stg mail" shortly.

-- 
Regards,
Pavel Roskin