fig-0.1.18 released

[Matthew Foemmel]

* Added "--update-if-missing" a.k.a "-m" option, which will only do an
update if the package is missing in the local repository (it won't
check timestamps for packages that already exist)

* "append" is now really a "prepend" i.e. it puts the value at the
beginning of the path. This is to help deal with the case where an
executable already exists on the user's PATH, but needs to be
overridden in the package.fig file. The name "append" will eventually
be deprecated - use "path" or "add" instead.

* "fig --list" no longer throws a stack trace if there's a package.fig
file in the current directory