[cairo] Proposal to disable PDF and PS backends by default for 1.0

[Tor Lillqvist]

If you disable them, please remember to take out
-DCAIRO_HAS_PS_SURFACE and -DCAIRO_HAS_PDF_SURFACE from the cairo.def
rule in src/Makefile.am... otherwise 1.0 will have a misleading
cairo.def in the tarball.

--tml