warn in em++ if PYTHON is not defined properly
aim for more evenly-sized pieces in outliner
fix test_exit_stack
 - moved enet tests and relay script
 - added support for SOCKK define to override ports when compiling
Remove errno codes that don't exist in musl.
Provide additional errno messages.
Remove some errno settings.

This is a follow up to the previous commit that removed them from
src/library.js.
 - fixed support for passing source to btest
 - added force_c option to btest
removed pids_to_clean global
 - removed test_sockets
 - removed test_sockets_bi_*
 - removed soon to be redundant test_sockets_select_server_closes_connection
updated and temporarily disabled test_sockets_gethostbyname
 - converted all socket tests to use C for the server-side
 - added new echo client / server test
 - updated websock harness and added new CompiledServerHarness to help run tests on multiple backends
 - merged FS and VFS namespaces
 - split off fs, memfs, sockfs and tty libraries
Merge pull request #1494 from waywardmonkeys/errno-changes

Errno changes
updated paths to be compatible on non-unix environments
removed bad comments
Merge pull request #1495 from inolen/websocket_tests

more websocket test updates
Merge pull request #1498 from inolen/lib_reorg

FS-related module reorganization
make test runner more lenient in parsing asm.js compilation message
fix bug in alcDestroyContext