Fixing linux incompatibilities introduced by MSVS fixes.

This version supports both MSVC tested with VS2010 and UNIX Makefiles on
Linux along with proper escaping for both.

making the custom command env variables test harness cross-platform

Switching VS10 custom command env to use cmake -E env

Switching VS10 custom command env to use cmake -E env

Fixing CustomCommandEnvVariable test cases

Fixing merge error
Cleaning up MSVS generator, adding proper escaping to cmCustomCommandGenerator::GetCommand
Cleaning up MSVS generator, adding proper escaping to cmCustomCommandGenerator::GetCommand
Cleaning up MSVS generator, adding proper escaping to cmCustomCommandGenerator::GetCommand