This includes code for sharedcache lookup and eviction.

We don't use workfile manager as a cache, we only keep workfiles around for
as long as we need them. So "clearing the cache" should always be a no-op.

If there is a schema in the database that the user does not have access to,
doing "select * from gp_toolkit.__gp_user_tables_readable" throws a
permission denied error on the schema. Use the relation-OID-variant of
has_table_privilege() function, to work around that.

Usage: minirepro <database> [options]

Options:
  --version             show program's version number and exit
  -?, --help            Show this help message and exit
  -h HOST, --host=HOST  Specify a remote host
  -p PORT, --port=PORT  Specify a port other than 5432
  -U USER, --user=USER  Connect as someone other than current user
  -q QUERY_FILE         file name that contains the query
  -f OUTPUT_FILE        minirepro output file name

Closes #157.

Use the standard initdb mechanism for it, instead of having bespoken code
in gpinitsystem.

Also remove the unnecessarily complicated logic to generate gp_toolkit.sql
from gp_toolkit.sql.in. All the JETPACK_* variables were constants, and
there is particular need in making the gp_toolkit functions relocatable to
different schemas or prefixes, so just hardcode them and remove the sed
magic.

Rewrite the file header of gp_toolkit.sql. The legal blurp is not needed,
make the header look more like that of information_schema.sql and
system_views.sql.

Remove compaction_info.sql. It was only needed for old in-place
upgrade from 4.3.x to 4.3.4.2, which is not relevant for master branch.

Fix the "jetpack" bugbuster regression test. It was originally written to
test the gp_toolkit views, but gp_toolkit was in fact not installed in
bugbuster, and the expected output just contained a bunch of "relation
does not exist" errors. Now it actually tests gp_toolkit again. Some of
the test queries didn't produce repeateable results, due to differing oids,
differences in table sizes, and other tables created by previous tests, so
fixed those too.

This has a small user-visible difference: gp_toolkit schema is now also
installed in template0. That caused the difference in the expected outputs:
pg_regress creates the "regression" database using template0 as the
template, so gp_toolkit used to not be installed in it, but it is now.