Linux: Handle protected_regular in inplace writes (#241)

Linux: Handle protected_regular in inplace writes (#241)

The Linux fs.protected_regular sysctl setting could cause rsync to fail to write a file in-place with the O_CREAT flag set, so the code now tries an open without O_CREAT when it might help to avoid an EACCES error.  A testsuite script is included (and slightly improved by Wayne to ensure that it outputs a SKIP when fs.protected_regular is turned off).