[cairo] Lots of endian issues in librsvg

[Andreas Falkenhahn]

Hi,

I noticed that the rsvg-filter.c part of librsvg has quite a lot of endian issues.
Many filters expect data to be present in BGRA byte order, but on big endian
systems data will be in ARGB order, of course. 

I've fixed all endian issues that I came across while playing with librsvg on a PPC
system. I used librsvg 2.26.0 as the base version. rsvg-cairo-draw.c also needs
a fix but this is merely a single line.

Here are my modified versions so someone can review the changes and
include the fixes in the master version:

http://www.falkenhahn.com/rsvg-filter.c
http://www.falkenhahn.com/rsvg-cairo-draw.c

Greets,

Andreas
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"Remember: It's nice to be important but it's more important to be nice!"