Log Message:
Update libmpcdec to 1.2.6.
While here, add DESTDIR support.

1.2.6
   * Fix an infinite loop regression from 1.2.3
   * Fix possible noise at the beginning of files

1.2.5
   * Properly increase API version since it has changed since 1.2.3
     Apps compiled with 1.2.2 WILL BREAK when used with 1.2.3 & 1.2.4 libs \ 
installed