'glob' returns FALSE on some PHP installs causing foreach error

[_ck_]

Unfortunately ​changeset 1089 was not enough.

Some PHP installs return a boolean FALSE when there are no glob matches. This loads the error log with warnings on the foreach every time bbPress is loaded.

Suggested (and tested) fix example:

// Load Plugins
if ( function_exists( 'glob' ) && is_callable( 'glob' ) && $glob=glob(BBPLUGINDIR . '_*.php') )
	foreach ( $glob as $_plugin )
		require($_plugin);
unset($_plugin);
do_action( 'bb_underscore_plugins_loaded' );
unset($glob);

[sambauers]

(In [1125]) Better glob validity testing. Fixes #787. Props _ck_

[sambauers]

(In [1126]) Better glob validity testing. See #787. Props _ck_

Also moving PHP version requirement to 4.3 in branches 0.8