Reduce update overhead during install and commit operations

[blee]

confman 'install' and 'commit' operations generate significant overhead updating the entire working copy (including modules that do not pertain to the host). This does not scale well when there are a large number of modules in the repository that are not included in the host's recipe.

One way to reduce this overhead is to only update modules included in the host's recipe. Naturally, the recipe should be updated before it is examined.

[joshu]

(In [511]) Adds an $UPDATE_RELEVANT_ONLY option to confman.conf that updates only
recipe-relevant files during commit/install.

See #10

[joshu]

(In [512]) Changed 'confman update' so that it no longer has the (undocumented) feature of
passing any arguments on to 'svn up' wholesale. After discussion with ccowart,
we determined that -r is really the only argument that needs to be passed to
'svn update'.

'confman update' now takes an optional argument of a recipe name; if no recipe
name is supplied, the default behavior is to update the entire repository. If
$UPDATE_RELEVANT_ONLY is set to true, however, the default behavior is the
equivalent of 'confman update $RECIPE_NAME', and a full repo update can be
achieved with 'confman update -a'. I also updated the documentation and manpages
to reflect these changes.

See #10

[joshu]

(In [519]) Addresses blee's worries about a race condition in confman updates by specifying
a revision using the -r flag for svn.

See #10.

[blee]

(In [565]) Merge fix for #10 into confman-1.9.

Closes #10