Make open_basedir default to empty, as per Zend.

Fixes #1749.
Revert "Make open_basedir default to empty, as per Zend."

This reverts commit e06f2643d6d27a857ce4c8f8383614cb7d2fdccc.
Handle ini_get and ini_set for open_basedir taking SafeFileAccess into account.

Addresses #1749.
Follow Zend, and disable open_basedir by default.

We can explicitly override this using the normal ini_set, or enabling safe_file_access and setting the allowed_directories.
Forgot to update the number of chars.
Store a copy of the open_basedir configuration for every request.
Use the context configuration for open_basedir.
Do not default to having the upload directory as part of the allowed set of directories.
Store the allowed directories in the execution context as a string vector, like the global runtime configuration.
Update the corresponding mutators/accessors.
Properly store the paths set via open_basedir.
Fix proper API usage.