Pester testsuite fixed including a fix for issue #122.

The testsuite does not polute the environment-variables and the PSModulePath anymore and the ModuleHash tests avoid issues cause git line ending transformation.

Testsuite was broken at least since merge in commit  fe2cc3f33182e4f384c81e5fb5210c9b6ea174fc.

Testsuite runs in an elevated shell with Powershell v2 and v3.
Merge pull request #134 from flofreud/fix-test-suite

Pester testsuite fixed including a fix for issue #122
Refactoring of PsGet.psm1 with the goals:
- unification of code style
- matching style recommondations for PowerShell (eg function names following the approved verb convention also internally)
- reduction of duplicate code (e.g. DownloadModuleFromWeb and DumbDownloadModuleFromWeb)
- less implicit dependencies between the miscellaneous functions considering error checking and handling
- documentation of expectations on function users
- removing all cases where errors did not cleanup afterwards leaving temp-files

Change in functionality:
- preserve the default PSModulePath if the environment variable is not defined for user or machine on persisting

For code style is more or less:

* Language keywords lowercased
* Function and variable cased like defined
* Function parameters begin with a uppercase
* Local variables with a lowercase
* Braces are placed like in C#
* SYNOPSIS of a function is places at top
	* Function top is easier to find as the end for reference
* Double quoted string are only used if format is necessary to signal that the string use format

Considered Links:
[http://ramblingcookiemonster.wordpress.com/2013/12/08/building-powershell-functions-best-practices/]
[http://msdn.microsoft.com/en-us/library/ff926074.aspx]
[http://windowsitpro.com/blog/my-12-powershell-best-practices]
[http://stackoverflow.com/questions/2025989/what-is-the-recommended-coding-style-for-powershell]
[http://blog.octo.com/en/powershell-v2-my-best-practices/]
Refactor the tests to a more consistent code style and improved the isolation of the tests. No temp files or environment variable changes remain after test execution anymore.
Merge pull request #135 from flofreud/cleanup-refactoring

Cleanup refactoring
added testmodules for post-install-hook extensions