Set MPI wrappers after confirming the package needs to be built

Because the cleaning of environment variables is only after the building
of a package, so MPI related stuffs should be only set when a package
needs to be built.
Add donation message
Bad README.md format
Fix default flags usage
Fix all_instances bugs

Also try to use wget to download packages if curl fails.
Let user set download_command in config file

User now can choose to use curl (default) or wget to download files.
Fix create_cmake_config method

Also add compiler_support_openmp? method.
Merge branch 'master' of https://github.com/dongli/packman
Fix small error
Merge branch 'master' of https://github.com/dongli/packman
Fix Boost and Mlpack

Set Boost_NO_BOOST_CMAKE to ON to let CMake find out what libraries to
link for us!
Add Ncview
Remind user to set defaults in config file if not yet set
Add more package checks in X11
Fix a bug

I wrote wrong compiler command matching pattern, should add '\b' to
detect word boundaries.
Release 1.0.0-a6
Merge branch 'release/1.0.0-a6'
Merge tag '1.0.0-a6' into develop

Gather some bugfixs and Cygwin supports