Add TAP tests for pg_dump

This TAP test suite will create a new cluster, populate it based on
the 'create_sql' values in the '%tests' hash, run all of the runs
defined in the '%pgdump_runs' hash, and then for each test in the
'%tests' hash, compare each run's output the the regular expression
defined for the test under the 'like' and 'unlike' functions, as
appropriate.

While this test suite covers a fair bit of ground (67% of pg_dump.c
and quite a bit of the other files in src/bin/pg_dump), there is
still quite a bit which remains to be added to provide better code
coverage.  Still, this is quite a bit better than we had, and has
found a few bugs already (note that the CREATE TRANSFORM test is
commented out, as it is currently failing).

Idea for using the TAP system from Tom, though all of the code is mine.