use call to run wget and curl

When wget or curl are wrapped in a .bat or .cmd file as is done by chocolatey then you have to run with call. Using call to run regular executables works as well. This prevents the error "The system cannot find the batch label specified" from appearing.
Merge pull request #1599 from samuelbosch/master

use call to run wget and curl
Merge remote-tracking branch 'upstream/master'