Regression test suite for cairo.

Using this test should be as simple as running:

	make check

assuming that the cairo distribution in the directory above has been
configured and built. The test suite here goes through some effort to
run against the locally compiled library rather than any installed
version.

The test suite needs to be run before any code is committed and before
any release. Here are the rules governing the use of the suite:

Before committing
-----------------

All tests should return a result of PASS or XFAIL. The XFAIL results
indicate known bugs. The final message should be one of the following:

	All XX tests behaved as expected (YY expected failures)
	All XX tests passed

If any tests have a status of FAIL, then the new code has caused a
regression error which should be fixed before the code is committed.

When a new bug is found
-----------------------
A new test case should be added by imitating the style of an existing
test. This means adding the following files:

	new_bug.c
	new_bug-ref.png

Where new_bug.c is a minimal program to demonstrate the bug, following
the style of existing tests. The new_bug-ref.png image should contain
the desired result of new_bug.c if the bug were fixed.

Makefile.am should be edited, adding new_bug.c to both the TESTS and
XFAIL_TESTS lists.

When a new feature is added
---------------------------
It's important for the regression suite to keep pace with development
of the library. So a new test should be added for each new
feature. The work involved is similar the work described above for new
bugs. The only distinction is that the test is expected to pass so it
should not be added to the XFAIL_TESTS list.


When a bug is fixed
-------------------
The fix should be verified by running the test suite which should
result in an "unexpected pass" for the test of interest. Rejoice as
appropriate, then remove the relevant file name from the XFAIL_TESTS
variable in Makefile.am.

Before releasing
----------------
All tests should return a result of PASS meaning all known bugs are
fixed, resulting in the happy message:

	All XX tests passed

