Pin the version of distribute
dx describe --name now prints names for all matches and exits with a nonzero exit code if no matches were found
Add basic tests for dx-build-app/let.
dx-build-app/let abides by exit code conventions.
Make dxclient tests not echo entire output of shell commands.
Don't barf on malformed execDepends.
Rename AppletBuilderException => AppBuilderException
PTFM-5908 Skip an appletDescribe call that was not really needed.

The appletDescribe call was problematic because it was the only data
object method that needed a project and didn't have one explicitly set
by us.
PTFM-6077-sidenote: adding delimiter between size string and "sponsored by DNAnexus" string
Merge branch 'master' into PTFM-2681-R-API-wrappers
PTFM-2681: adding build instructions to the Readme