Todo

Ability to specify the default prefix, for example: Macports uses /opt/local Homebrew uses /usr/local Ubuntu use /usr

Users can specify the prefer one when running init command.
```
  phpbrew init --prefer-prefix=macports
```
When configuring php
Ability to switch curl, wget or pure php downloader.
Smarter build tasks
- xdebug (enable zend extension with absolute path)
- build with extensions
Mirror option
Separate install command to sub-tasks, so we can run tasks separately
- Fetch command.
- Build command.
- Install command.
- Test command.
Inherit option
- Copy variants from previous install.
- Copy config file from previous install.
Extra variants: Add extra variant type for non-configure options:
- phpunit variant
- zendframework variant
- pyrus variant
- xdebug variant
- apc variant
Fallback handler when DOMDocument is not found.
pure bash support.
PHP 5.2 compatibility (or pure bash script?) Phar requires PHP 5.2.0 or newer. Additional features require the SPL extension in order to take advantage of iteration and array access to a Phar's file contents. The phar stream does not require any additional extensions to function.

Done

x variant sets x Extension Builder x Extension disable/enable command x --patch={file} option support.