Make line endings in unit tests portable

Some unit tests are failing on *nix like OS's due to unit tests
having hard coded windows line endings in assert string constants.

This commit replaces instances of "\r\n" with platform agnostic:
Environment.NewLine
TRAVIS: install gtk-sharp2, but not nunit

I got the gtk-sharp package name wrong.

Also, since nunit is already checked in under tools, we don't need to install it.
TRAVIS: use forward slash when building.
travis.yml.

- run `apt-get` during `before-install`, per Travis docs. (http://about.travis-ci.org/docs/user/build-configuration/)
- run `apt-get` with -qq. This implies -y, so it won't stop to prompt.
- run nunit under mono
- run nunit that is already checked in under tools
Use forward slashes in Pash.nunit.

This is apparently required to run on Linux, and tolerated when running on Windows.

This was sent by Andrew Barnes (@b333z).
Use relative path in Pash.nunit.

An absolute path from a devs machine is an abomination! NUnit generated it this way. *sigh*

This was sent by Andrew Barnes (@b333z). Thanks!
Merge branch 'lineend-test-compat' of https://github.com/b333z/Pash2 into travis2
FORMATTING: Reformat code that @b333z sent over.

These are fine changes, I just wanted to run the Visual Studio formatter over them ASAP.
Work around a Mono C# compiler crash.

The original code would trigger a crash in the Mono C# compiler, e.g.:

    ArrayExpressionAst.cs(23,43): error CS0584: Internal compiler error: Object reference not set to an instance of an object

Moving this expression to its own method does the trick.
Build `TestHost` with non-client framework profile.

This was generated this way by Visual Studio, but my MonoDevelop installation on Ubuntu doesn't have the Client configuration, causing a build error.
Take advantage of `.travis.yml` to document how to build.
Disable warnings as errors

The commit fixes issue JayBazuzi/Pash2/issues/23 by adding
an attribute to stop xbuild/mono treating warnings as errors.
Merge branch 'fix-warn-error' of https://github.com/b333z/Pash2 into travis2-wx
warn-as-error only on Windows
Merge branch 'travis2-wx' into travis2

# By Andrew Barnes (1) and Jay Bazuzi (1)
* travis2-wx:
  warn-as-error only on Windows
  Disable warnings as errors
Merge branch 'travis2'

# By Jay Bazuzi (10) and Andrew Barnes (2)
* travis2:
  warn-as-error only on Windows
  Disable warnings as errors
  Take advantage of `.travis.yml` to document how to build.
  Build `TestHost` with non-client framework profile.
  Work around a Mono C# compiler crash.
  FORMATTING: Reformat code that @b333z sent over.
  Use relative path in Pash.nunit.
  Use forward slashes in Pash.nunit.
  travis.yml.
  TRAVIS: use forward slash when building.
  TRAVIS: install gtk-sharp2, but not nunit
  Make line endings in unit tests portable