Implemented support for running triggers with binpkgs.

Also the following changes were made:
 * Added an info-files trigger, to (un)register info files.
 * xbps-base-dirs: it's responsible to install triggers on destdir.

--HG--
extra : convert_revision : 8d707053616f38d2b5beef7cf28e1bc4a66812b8

doc/TODO

@@ -4,8 +4,6 @@ xbps-src:
    Something like ${sourceforge} to pick up any specified mirror on the list.
  * Add support to run INSTALL/REMOVE scripts, so that the same actions are
    performed in source/bin packages. [STOPPED]
- * Use current postinstall_helpers to automatically add triggers, shared
-   by src/bin packages. [IN PROGRESS]
 
 Packages:
  * fix mpfr hardcoded rpath for gmp.
@@ -19,7 +17,6 @@ xbps-bin:
  * Add support to update packages.
  * While installing a package, check if version that is going to be
    installed is already installed.
- * (Un)register info files automatically. [IN PROGRESS]
 
 xbps-repo:
  * Replace binpkg-genindex.sh with a target for xbps-repo to generate the