chflags support added

Initial chflags(2) support has been added to the repository. This support has not been integrated with the ext2 flags support, although there is some feature overlap. This has been tested on Mac OS X 10.4 and Fedora Core 5 i386. Please feel free to test and let the list know how it goes.

To elaborate on chflags(2) vs ext2 flags, here is what each looks like in the toc:
ext2 flags:

<attribute>
     <NoDump fstype="ext2"/>
</attribute>

chflags(2):

 <flags>
     <UserNoDump/>
 </flags>

Clearly nodump has similar meaning between these two representations. The obvious desire is to have a mapping engine within xar "just know" that chflags nodump is the same as ext2's nodump. Similar with some of the immutable bits.