For PECL extensions that are linked into PHP, the license
must be compatible with the PHP license. That means you can not GPL
a PECL extension or you would be violating the GPL. Note also that if
you write an extension that links against a GPL'ed library you will be
violating the GPL. If you need to link against a GPL'ed library, get
permission from the author of the library.
To set the license of you PEAR/PECL package, put it in the head of
all source code files of your package and also the type of it
inside the <license> tag of your package description file
(package.xml).
