Unittest - Add prefixes to task and taskd temporary folders
Unittest - Add mechanism to skip task and taskd tests

* When testing multiple clients vs server versions, repeating client
tests is unnecessary. By setting the env variables TASKW_SKIP and
TASKD_SKIP it will now be possible to skip all task (client only) and
taskd (client + server) tests, respectively.
Unittest - Make is easier to reset env vars of task and taskd
Unittest - Implement faketime for use in taskw
Unittest - Add test example using libfaketime
Unittest - Skip tests that use faketime if not available
Unittest - Add a memoize function for caching of function results
Unittest - Memoize utils.which for faketime speedups
Unittest - Use stderr for diagnostics too
Unittest - Buffer stdout/stderr until after test status is printed
Unittest - No longer necessary to prefix strings with hash
Merge pull request #11 in TM/task from ~UNODE/task:2.4.0 to 2.4.0

* commit 'c5d4efd4d2cdc48489193eee45c2a9566dc6b2fd':
  Unittest - No longer necessary to prefix strings with hash
  Unittest - Buffer stdout/stderr until after test status is printed
  Unittest - Use stderr for diagnostics too
  Unittest - Memoize utils.which for faketime speedups
  Unittest - Add a memoize function for caching of function results
  Unittest - Skip tests that use faketime if not available
  Unittest - Add test example using libfaketime
  Unittest - Implement faketime for use in taskw
  Unittest - Make is easier to reset env vars of task and taskd
  Unittest - Add mechanism to skip task and taskd tests
  Unittest - Add prefixes to task and taskd temporary folders