Miscellaneous cleanups within tests and support library.

[albu-diku]

• make all tests import tests.support and thus remove sys.path fiddling
• move cleanpath() ensure_dir argument to temp_path() and collapse them
• remove outputpath() function
• add assertFileExists() assertion and use it to sinplify callsites
• silence junk printed to stdout due to code coming under test that directly calls print()
• use assertRaises() in place of hand rolling assertion capture in tests for some of the jupyter related logic
• apply review notes to recently added transferfunction locking tests and attempt to clarify cases via a common setup block and some splitting

[jonasbardino]

Merged through svn with a couple of minor modifications mentioned in review.