Also some small fixes to make the PBXT testsuite work in --embedded.

config/ac-macros/plugins.m4:
  MYSQL_PLUGIN_DEPENDS_ON_MYSQL_INTERNALS macro extended to support multiple files.
mysql-test/std_data/pbxt_load_unique_error1.inc:
  Move file to be accessible also for testing embedded server.
mysql-test/suite/pbxt/r/pbxt_bugs.result:
  Fix LOAD DATA LOCAL INFILE path so it works also for testing embedded server.
mysql-test/suite/pbxt/t/pbxt_bugs.test:
  Fix LOAD DATA LOCAL INFILE path so it works also for testing embedded server.
mysql-test/suite/pbxt/t/pbxt_locking.test:
  Disable for embedded, as it needs SHOW PROCESSLIST functionality not available there.
mysql-test/suite/pbxt/t/pbxt_transactions.test:
  Disable test for embedded, as it needs ability to connect from outside (mysqldump).
mysql-test/suite/pbxt/t/ps_1general.test:
  Fix replace_result for new mysql-test-run.pl.
sql/sql_plugin.cc:
  Remove hack that disables PBXT in embedded.
storage/pbxt/plug.in:
  Fix crash in PBXT in embedded server.
storage/pbxt/src/Makefile.am:
  Remove not needed CFLAGS/CXXFLAGS (they cause autotools to generate different object names, which in turn cause the MYSQL_PLUGIN_DEPENDS_ON_MYSQL_INTERNALS replacement of object files inside library files not to work).
storage/pbxt/src/ha_pbxt.cc:
  Ugly hack to allow more threads in embedded server (need a better fix I think).
storage/pbxt/src/table_xt.cc:
  Use stderr for logging not stdout (prevent spamming --embedded test suite output with stray messages).
storage/pbxt/src/thread_xt.cc:
  Use stderr for logging not stdout (prevent spamming --embedded test suite output with stray messages).
storage/pbxt/src/trace_xt.cc:
  Use stderr for logging not stdout (prevent spamming --embedded test suite output with stray messages).