The Hive code is pulled in via an SVN external definition.  This allows 
us to have a local version of hive to build against, including an 
up to date trunk version, without needing to fork the code.

The external definition is pegged to an SVN revision, so that 
changes in Hive's code base do not cause suprising changes in HCatalog.  
The SVN revision should be updated regularly.

For release branches, the SVN revision should be pegged against a Hive release
tag.

The external definition can be edited by doing:

svn propedit svn:externals hive

in the top level directory.