Added new SignToolHelper
first pass at adding distributed file logger support

made the logger stringification common.
tweak the distributed logger string generation some

tested via my own test fsx
semicolon delimiters for msbuild distributed logger parameters
Implemented old SignHelper method

Added the old method provided by the old SignHelper and marked it as obsolete. Renamed the properties "File" and "Password" of the SignCert type to "CertFile" and "PasswordFile" to make it more clear what they mean. Also added documentation to those properties.
Issue #541: look first in default path for a tool, and only if it was not found there start the search from the root.
Merge pull request #542 from Slesa/develop

Issue #541: look first in default path for a tool
Merge pull request #535 from Bomret/feature/signtoolhelper

Added new SignToolHelper
Merge pull request #536 from baronfel/msbuild_dlogger

Add support for MSBuild Distributed Loggers
Merge branch 'develop' of https://github.com/fsharp/FAKE

Conflicts:
	src/app/FakeLib/Globbing/FileSystem.fs