Various fixes:
Various fixes:

1. imgp->image_header needs to be cleared for the bp == NULL && `goto
   interpret' case, else exec_fail_dealloc would free it twice after
   an error.

2. Moved the vp->v_writecount check in exec_check_permissions() to
   near the end.  This fixes execve("/dev/null", ...) returning the
   bogus errno ETXTBSY.  ETXTBSY is still returned for attempts to
   exec interpreted files that are open for writing.  The man page
   is very old and wrong here.  It says that ETXTBSY is for pure
   procedure (shared text) files that are open for writing or reading.

3. Moved the setuid disabling in exec_check_permissions() to the end.
   Cosmetic.  It's more natural to dispose of all the error cases
   first.

...plus a couple of other cosmetic changes.

Submitted by:	bde

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase