build.xml updated to cooperate more with Github.

Added "gitupdate" target and removed "build.webstart" and "cvsupdate"
targets.

This branch is working under the assumption that you have something
like a McIDASV "project" directory. In other words:

/mcidasv-project
    IDV/ # https://github.com/Unidata/IDV.git
    addeservers/ # mcx binaries
    idvlib/ # idv jars
    install4j/
    jh2.0/ # javahelp
    mcidasv/ # https://github.com/mcidasv/mcidasv.git

[0]
Updated paths.

Used relative paths…not exactly thrilled about it, either. [0]
Updated paths.

No more hardcoded locations. [0]
Updated .gitignore to ignore things routinely generated by a build. [0]
Adding Ant targets for the various scripts that generate ancillary parts of a nightly build [0]
Updated paths.

Attempting to replace all hardcoded paths with relative paths. [0]
Removed duplicate "packsource" target. [0]
Fixed paths. [0]
Updated paths.

No longer using hardcoded paths. [0]
Git equivalent to proc_mcv_docs.php [0]