Add current_path() setter, !#800, change form of some includes in response to bug report !#600

svn path=/branches/libs/filesystem/filesystem/; revision=38912
Add recursive_directory_iterator test cases to convenience_test.cpp, fix !#1061 plus a pop() bug detected by new tests

svn path=/branches/libs/filesystem/boost/filesystem/; revision=38978
Fix !#1073. Also reinstate changes from two prior versions dropped inadvertently by revision 35823.

svn path=/branches/libs/filesystem/filesystem/; revision=39002
Get rid of non_posix_equivalent, fix Jamfiles, fix Linux typos, refactor so basic_filesystem_error::what() works on compilers that screw up member specializations 

svn path=/branches/libs/filesystem/filesystem/; revision=39133