Fail fast if there is an exception thrown while instantiating an asset
file.
Clean up of code around asset creation and initialization since it
wasn't obvious why assets had to be initialized with a file object,
given that they may be associated with any number of underlying files --
it turns out that this parameter can be used for either a single file or
a directory, and this is okay since it's effectively under plug-in
control.
Allow asset classes to throw an AssetFileInstantationException during
their initialization method.
AssetLocation.requirePrefix() method, since each source module was
previously performing calculations that were part of the asset locations
domain knowledge.
Renamed 'mypkg' to 'appns' within all of our tests in preparation for
enforcing class namespaces.
Allow AssetLocation.requirePrefix() to throw RequirePathException
exceptions.
Re-arranged method to be more consistent with how I usually do it.
Added some TODOs.
Ensure the default asset plug-in appears last in the list so that other
plug-ins that can conclusively recognize qualifying asset locations will
be matched first.
Implement requirePrefix() on ChildSourceAssetLocation, as this will need
to give a different result, as the 'src' directory is not part of the
require path.
Adding an specific exception for completely invalid require paths, which
will be needed once we start enforcing class namespaces.
Start returning different asset locations for BladeRunnerJS third-party
libraries.
Fixed bug in ChildSourceAssetLocation.requirePrefix().
Converted test I missed earlier to use 'appns' rather than 'mypkg'.
Started appending the container require prefix to all require paths.
This commit includes the following related changes:

# Removed the leading forward slash from require paths as this actually
signifies a file path rather than an absolute require path as might be
expected.
# Made conformant BRJS code throw an exception if classes aren't
correctly namepaced as this would otherwise prevent us from having
require paths that are freely convertible to namespaced names.
# Updated all tests that created incorrectly namespaced classes.
Improved the failure message when assetLocationHasDependencies() is used
with an asset location that doesn't exist.
Minor whitespace improvement.
Added TODO.
Moved class into correct package.
Removed unnecessary asset location within brjs conformant libraries.