Merge pull request #96 from pullrich/master

Fix a typo.
TestDrive implemented

The test drive is created in describe and when moving to Context its
"state" is saved. When moving from the context files created in context
are deleted. This is done purely on full path basis so changes made in
context to Describe-scope files are kept. All test drive functions moved
to TestDrive. All tests regarding the test drive  moved to
TestDrive.ps1. Change to the Global scope polluting test were needed.
The test is not working properly anyway.  :(
this should fix the build. weird 3.0 and 2.0 differences
Random directory for TestDrive.

Test drive is set to random directory. The global $TestDrive variable
and global PSDrive TestDrive are still published but now the Pester
should not step on its own toes when executed in two separate processes
at the same time.

making tests work if env:temp ends with a slash

updating CHANGELOG
Merge branch 'random_testdrive_dirs'
Merge branch 'umaster' into mergetest