`build` command parsed as a flag when using sandbox named `build`

[acfoltzer]

When using a sandbox directory called build, the cabal build command is somehow misinterpreted:

$ cabal-dev -s build configure
Resolving dependencies...
Configuring foo-0.1.0.0...
$ cabal-dev -s build build
cabal: Unrecognised flags: build

However, specifying no sandbox, or a sandbox of a different name, seems to make everything work.

$ cabal-dev -s cabal-dev configure
Resolving dependencies...
Configuring foo-0.1.0.0...
$ cabal-dev -s cabal-dev build
Building foo-0.1.0.0...
Preprocessing library foo-0.1.0.0...
Registering foo-0.1.0.0...