Various restructure of test framework handling of paths to avoid duplicate path editing which caused failed tests. Adjust many tests to deal with added subdirectories in build outputs now that toolset requirements are active.
Related changes:
* BoostBuild.Tester & TestCmd.TestCmd interfaces now accept external process parameters as a list of strings, thus avoiding problems with parsing arguments containing spaces.
* Avoided a potential process hang in case an external process being run prints out enough output to fill up the OS's pipe buffer (OS would pause the process until someone read the data from the pipe but the testing framework would not do this until the process in question had terminated).
[SVN r79448]
bjam --clean some_main_target
don't clean files belonging to other main targets, even if those other main
targets are dependencies of 'some_main_target'.
[SVN r32760]
