first prep for rel files proxying through bufcmd
factor out open parameter options parsing
fs server version of relative file support
more work on REL files, open now passes from firmware to server and back
fix crash when no options were sent
more work on rel files
separate block provider from relfile provider
more work on REL files for fs_provider
(tests up to reltest3(.b), test G work)
more REL file test cases
more work on REL files
Simplify channel_get() and provider place for provider shortcut to channel_get and channel_put
move relfile read/write code into channel shortcuts
Fix write with offset, write over end of record
passes reltests 1-4
rel files with fs_provider pass all current tests
Merge branch 'relfiles' of github.com:fachat/XD2031

REL files should now work on fs_provider. At least passes all my tests.

Conflicts resolved:
	pcserver/curl_provider.c
	pcserver/di_provider.c
	pcserver/fs_provider.c
	pcserver/tcp_provider.c
Merge remote-tracking branch 'origin/master' into fatfs