opening php.ini anomaly

Hi, I came across a minor bug related to where php.ini file is located. From what I see in configuration-parser.y, php tries to open php.ini in the following places: first, in the current directory, second, in directory specified in PHPRC variable, and third, in hard-coded place (/usr/local/lib by default or specified via --with-config-file-path at compile time). First, such behaviour should be indicated clearly in documentation. Second, when the PHPRC variable is not set, it is treated like empty string, which caused the file /php.ini to be opened (which caused me today some headache :). The attached patch is supposed to fix that (empty variable case that is, not documentation :). -- Be well, Pasha.