W2j import/include caching

[Steve Green <st...@epok.net>]

Developers,

I've added a feature to SymbolTable and W2j such that it will cache
downloaded imports (and includes) to a directory specified on the
command line (-C <dir>).  Subsequent regens will find the cached files
and not have to download them again.  This is useful for us since we
sometimes have to generate code when we are offline (like on a plane) or
behind a slow link or when the referenced xsd is offline (rare, but it
happens).  It's also very convenient for locating the offending xsd file
when W2j spits out the error about a type being referenced but not
defined.

If others find this feature useful, I will submit a patch.  Please
comment.

~S