[GH #641] Renable line-directives for pmc

line directives point to the real errors in the original source.
The generated c file is sorted. Rather fix debugging problems if there are any.
[GH #302] new config dynext_libs, new ENV var PARROT_DYNEXT, new add_env_paths()

On some systems a special library dir is in the cc library search, or added by -L to the libpath
but this path is missing from the loader configuration, so runtime dlopen attempts will fail.
Most prominently pcre on macports or fink, missing /opt/local/lib.
Hints may add a new key dynext_libs to add such a path to DYNEXT for loadlib.
Also provide a new PARROT_DYNEXT to manually set such paths for the runtime.
Add a helper function add_env_paths() to add multiple paths from an enviroment variable
to some library search path. Currently PARROT_INCLUDE and PARROT_LIBRARY only accept one path element.
(See #903)
[GH #302] special windows fixes, path_guarantee_trailing_separator

windows adds ./ to dynext to be explicit about the windows loadlib order (which does this)
Ensure trailing_separator during configuration and init.
[GH #302] more tests for single, multi or no add_env_path calls
[GH #302] reword last test
[docs][GH #302] Revise lib_search_path.t docs, dynext library search order
Merge branch 'rurban/pcre-dynext_libs-gh302'