Changes requested by Gentoo Bug #507512 comment #2.

Remove packaged PEAR libs and add rdepend for the portage versions:

  * dev-php/PEAR-Crypt_GPG (program/lib/Crypt)
  * dev-php/PEAR-Net_Sieve (program/lib/Sieve)
  * dev-php/PEAR-Net_Socket (program/lib/Net/Socket.php)

Also addressed bug #489970 by adding rdepend on dev-lang/php[filter].

https://bugs.gentoo.org/show_bug.cgi?id=507512#c2
https://bugs.gentoo.org/show_bug.cgi?id=489970