improve handling of default values

[mlorentz75]

• use regex to remove possible clutter from RDB$DEFAULT_SOURCE
• handle escaped single quotes in string-type columns
• attempt to handle most context variables for date/time columns:
  • recognize more context variables
  • handle optional precision in square brackets for CURRENT_DATE/TIME/TIMESTAMP

[robregonm]

Checking the code of the pull request..., do this mean that this extension will be fully working for Firebird 2.5 and above? If this is correct, then we need to update the README.md in order to add this minimum version requirement.

[mlorentz75]

The changes attempt to handle most context variables known in FB2.5 and that's currently the only release I'm testing against. I'm afraid I currently don't have time testing against older Firebird releases.

But I guess the patch shouldn't break things with former releases. Like, FB prior to 2.0 didn't have the optional precision in CURRENT_TIME (see: http://www.firebirdsql.org/refdocs/langrefupd20-current_time.html) so people running FB1.5 would just use 'CURRENT_TIME' without precision. The updated code would still work as it matches the beginning of the default value string.

That said, a note in README.md recommending to use the latest version of the Firebird PDO driver and probably DB too wouldn't hurt. I was quickly running into problems on CentOS 6 x86_64 when using the stock php-interbase RPM and thus switched development to FC18.

[robregonm]

It's ok, just wanted to make sure. I'll add the recommendation to the REAME.md file. Thanks.