reindent for clarity

Adding internal API to get environment variables for custom commands

Adding test for new custom command env setting

Updating other references to internal API changes

adding env_test program

updating env test to write out a product

polishing environment variable test case

Adding placeholder for env var list in cmCustomCommand

adding implementations for env variable support

changing env variables from vector of pair to map

adding support for environment variables in custom commands in UNIX Makefiles

fixing indentation

fixing indentation

fixing indentation

changing test variable name to be clearer that it's an example

fixing indentation

Switching over to using CMake -E instead of bash-like environment variable setting

ENV vars: improve source consistency (variable naming, etc.).

ENV vars: improve source consistency (variable naming, etc.).

Changing custom command environment variable argument from ENV to ENVIRONMENT

ENV vars: Document add_custom_command() ENVIRONMENT option.

ENV vars: fix cross-platform (MSVS) incompatibilities.

- std::fstream does not support std::string stream input
- need to obey additionally required CMAKE_CFG_INTDIR, too