optionally omit or trim path info stored in table files

[johnyf]

Parser production rules in PLY table files include path information (the p.file). This could be a security issue, because:

1. generating and including tables in a distribution archive makes the path public. So one either has to move to a neutral location (like /tmp) in order to produce a distribution, or they must not include the parser table files (requires unnecessary case selection in setup.py), or they disclose their local directory structure.
2. at installation time, on a multi-user system, if the tables are generated before copying to site-packages, then they will contain path information for the user that performed the installation. Others may have read access to site-packages, but not to the user's directories. (Thanks to @slivingston for describing this use case).

Reading through PLY's source code, it follows that the file path information is used only for error reporting, not for parsing functionality. It would be convenient if an option was made available in yacc.yacc to either:

• omit the path from the table file, or
• trim the path, keeping only the file name, so that error reporting functionality be affected less.

In any case, the paths reported for an installed package, whose tables were generated before copying to site-packages, will show incorrect path prefixes (preceding the package directory name).

[dabeaz]

Modified to only record the base filename in the parsetab.py file.