Also ignore config.h.in
Conditionally make some linux-only stuff
Core diod bits for OSX

 * dont set RLIMIT_LOCKS
 * emulate (poorly?) ppoll
Clean up various headers to work multiplatform
Fix various stat/statfs stuff and unsupported p9fs flags.
Fix directory traversal on OSX
Macro shim the l*xattr functions for OSX.
Fix logging of progname on OSX.

On OSX some things will stomp the pointer returned by basename(), so
strdup it for posterity.
Fix some mismatches between linux and OSX sockopts.
Jimmy in the Linux EOPNOTSUPP return code.

This is necessary for the expected v9fs UNLINKAT/RENAMEAT semantics.
Jimmp out the setfsuid stuff pending figuring out how to OSX it.
Sign work / Note what needs doing on OSX
update autoconf/makefiles to reflect conditionals