* The version string pattern is now:
<major>[.<minor>[.<micro>]][-<pre>][-<release>]
* Introduce B_HPKG_ATTRIBUTE_ID_PACKAGE_VERSION_PRE_RELEASE package
attribute.
* Add "preRelease" field to BPackageVersionData.
* Add "preRelease" property to BPackageVersion and packagefs's Version.
* Adjust package reader and writer code accordingly.