- Make 'pwd -L' fall back to 'pwd -P' if PWD is incorrect.
- Ignore PWD if it contains "/./" or "/../".
- Garbage collect some redundant code.
It is still non-conformant because posix mandates that the default
be 'pwd -L' (aka ksh), not 'pwd -P' (historic practise everywhere else).
Changing the default will break too much...
If stdout is a tty, use vis(3) to print any filenames to prevent garbage
from being printed if the filename contains control- or other non-printable
characters.
While here, sprinkle some EXIT_FAILURE and NOTREACHED where appropriate.
$PWD is unset in the environment and update usage() string; addresses
PR bin/7504.
* Fix whitespace lossage from rev. 1.11.
* Minor other cleanups, including EXIT_{SUCCESS,FAILURE}.
