xgettext: In language PHP, avoid stack overflow.
* gettext-tools/src/x-php.c: Include error-progname.h.
(MAX_NESTING_DEPTH): New macro.
(paren_nesting_depth, bracket_nesting_depth): New variables.
(extract_balanced): Increase and check paren_nesting_depth or
bracket_nesting_depth before calling extract_balanced recursively.
(extract_python): Initialize paren_nesting_depth and bracket_nesting_depth.
* gettext-tools/tests/xgettext-php-stackovfl-1: New file.
* gettext-tools/tests/xgettext-php-stackovfl-2: New file.
* gettext-tools/tests/xgettext-php-stackovfl-3: New file.
* gettext-tools/tests/xgettext-php-stackovfl-4: New file.
* gettext-tools/tests/Makefile.am (TESTS): Add them.
