tcsh segmentation faults in parser on trivial expression, error message not output on stderr

[B Bobo]

tcsh fails to parse null command substitution:

 % echo ``
Segmentation fault (core dumped)
 %

 % echo ````
Segmentation fault (core dumped)
Segmentation fault (core dumped)
 %

etc.

Additionally, the shell's own error message is itself written onto standard output, instead of standard error.

This is a regression. In tcsh-6.10 and earlier versions, the parser handles null command substitution correctly:

 % echo ``
 %

This bug has been confirmed to exist in tcsh-6.17.02 in Oneiric. No further details are currently available.