[libpeas] (18 commits) ...Merge remote-tracking branch 'gregier/fixes'

[Steve Frécinaux <sfre src gnome org>]

Summary of changes:

  5241a06... Free the loaded plugins hash table in the Seed loader
  b3af3a0... Fix handling invalid loaders
  655c6ba... Fix comment in Python plugin loader
  3db4dc4... Don't use interned strings in C plugin loader
  2cc0d36... Add testing_init() to libpeas-gtk's libtesting
  8313b08... Add a gcov make rule
  5bb4242... Don't use g_atexit() in the tests
  2aff50d... Add a test for an nonexistent search path
  9ec6b2e... Add a test for an invalid GKeyFile formatted PeasPluginInfo
  94174f6... Add tests for (un)loading plugins that are already (un)load
  9d19252... Add a test for an invalid loader
  44af1b0... Add an extension test for garbage collection
  6a0b340... Check that the extension GType is an interface
  439233d... Add tests for peas_engine_provides_extension()
  64c1874... Test multiple engine shutdown in the test case
  5fa94f3... Expand peas_engine_set_loaded_plugins() test
  7f193c7... Add .PHONY to Makefile.tests
  e659d2b... Merge remote-tracking branch 'gregier/fixes'