php: change config-file-scan-dir from /etc to /etc/php.d

By chance I noticed that php picked up my /etc/odbc.ini file (clearly
wrong!). This fixes it by adding a namespace for php.

WARNING: This is a breaking change for anyone that happen to rely on php
picking up .ini files from /etc.

pkgs/development/interpreters/php/default.nix

@@ -270,7 +270,7 @@ let
         done
 
         [[ -z "$libxml2" ]] || export PATH=$PATH:$libxml2/bin
-        ./configure --with-config-file-scan-dir=/etc --with-config-file-path=$out/etc --prefix=$out $configureFlags
+        ./configure --with-config-file-scan-dir=/etc/php.d --with-config-file-path=$out/etc --prefix=$out $configureFlags
       '';
 
       postInstall = ''