Add native and JS tests for escapeLiteral and escapeIdentifier.
Move string escaping tests to proper locations.
#403 Only use native escape functions if PG version >= 9.0.0. Otherwise use the JS functions.
Include pg_config.h to get PG_VERSION_NUM.
Include version 9.0.0 in escape function check.
Merge pull request #409 from rpedela/master

Fix build when escape functions are not supported in libpq