### Please describe the problem.

When trying to build git-annex 5.21050113 in a clean cabal sandbox on OSX and not having wget avalible, breaks the configure step of the build. See excerpt of build log below.

I am not sure if it is a bug or not, from the debian dependencies it seems that wget is required, but from reading various pieces of the documentation it seems to only be recommended. Installing wget makes it build. 

### What steps will reproduce the problem?



### What version of git-annex are you using? On what operating system?

5.20150113 on OSX Yosemite.

### Please provide any additional information below.

[[!format sh """
  checking version...fatal: Not a git repository (or any of the parent directories): .git
 5.20150113
  checking UPGRADE_LOCATION... not available
  checking git... yes
  checking git version... 2.2.1
  checking cp -a... yes
  checking cp -p... yes
  checking cp --preserve=timestamps... no
  checking cp --reflink=auto... no
  checking xargs -0... yes
  checking rsync... yes
  checking curl... yes
  checking wget... no
  checking wget supports -q --show-progress...setup: wget: does not exist
cabal: Error: some packages failed to install:
git-annex-5.20150113 failed during the configure step. The exception was:
ExitFailure 1


# End of transcript or log.
"""]]

-- Carl

> wget is not intended to be a hard build dependency. The Debian package
> should always be built with wget, so it's a build-dependency there.
>
> I've fixed the configure script to not crash in this situation.
> [[done]]. --[[Joey]]
