Description:
------------
The macports (http://www.macports.org) pecl cannot install the yaml extension 
because the extension's config.m4 (and generated configure script) look for yaml.h 
in /usr/include and /usr/local/include rather than in /opt/local/include.

The config.m4 script should use the result of 'php-config --prefix' (which is 
stored in $prefix) rather than (or in addition to?) the hard coded /usr and 
/usr/local.

The pecl script doesn't allow the user to pass "--with-yaml=/opt/local" to yaml's 
downloading yaml-1.0.1.tgz ...
Starting to download yaml-1.0.1.tgz (33,774 bytes)
configure so there is no workaround for this problem.

Test script:
---------------
% sudo pecl install yaml

Expected result:
----------------
downloading yaml-1.0.1.tgz ...
Starting to download yaml-1.0.1.tgz (33,774 bytes)
...
checking for yaml in default path... found in /opt/local
...
config.status: creating config.h
...

Actual result:
--------------
downloading yaml-1.0.1.tgz ...
Starting to download yaml-1.0.1.tgz (33,774 bytes)
...
Please provide the prefix of libyaml installation [autodetect] : 
...

checking for yaml in default path... configure: error: not found
ERROR: `/private/tmp/pear/temp/yaml/configure --with-yaml' failed