Merge from vendor branch BMAKE:

Merge from vendor branch BMAKE:
Import bmake-20100414:
- Resolve argv[0] with realpath if needed
- Add :tA to realpath(3)ify variables
- Support for .info, .warning, .error, .ERROR
- Unit tests for .ERROR / .error; never make .ERROR the default target
- Fix for .ALLSRC being populated twice
- Support for .MAKE_MODE, .MAKE.MAKEFILE_PREFERENCE, .MAKE_DEPENDFILE
- Haiku support
- Improved diagnostics for .for with multiple variables
- Rewrite bootstrap to not use make
- Fix for -m .../
- Add support for .unexport
- Catch typoes in .el*if etc
- Fix parsing of :S;...;...; applied to .for loop iterators appearing in
  dependency lines