Use http-conduit for url downloads by default, annex.web-options enables curl

* For url downloads, git-annex now defaults to using a http library,
  rather than wget or curl. But, if annex.web-options is set, it will
  use curl. To use the .netrc file, run:
    git config annex.web-options --netrc
* git-annex no longer uses wget (and wget is no longer shipped with
  git-annex builds).

Note that curl is always run in silent mode, since the new API for
download has a MeterUpdate and doesn't make way for curl progress
output. It might be worth writing a parser for curl's progress output
to update the meter when using it, but I didn't bother with this edge
case for now.

This commit was supported by the NSF-funded DataLad project.

Build/NullSoftInstaller.hs

@@ -9,7 +9,8 @@
  - for that.
  - 
  - To build the installer, git-annex should already be built to
- - ./git-annex.exe and the necessary utility programs (rsync and wget)
+ - ./git-annex.exe and the necessary utility programs
+ - (specifically rsync)
  - already installed in PATH from msys32.
  -
  - Copyright 2013-2015 Joey Hess <id@joeyh.name>