makechrootpkg does not pass on makepkg arguments when downloading sources

makechrootpkg does not pass on makepkg arguments to makepkg when downloading sources. This makes it impossible to download sources through proxies with environmental variables like ALL_PROXY.

One way to address this is to just add those arguments there, but this might break other people's workflow. Here's my patch that uses [ENVVAR=value] [ENVVAR+=value] when downloading sources. 0001-add-environmental-variables-to-verifysource_args.patch