vpnc-script fixes

• Handle nil keyboard interactive auth

This is the old v4.0.15 release spruced up with newer Go and build process.

Update dependencies, build with gb.

• Fix crash at startup when running non-root on Linux
• Fix crash at startup when unable to increase number of fd:s
• Fix crash at startup when missing ~/.mole

• Minor bugs fixed (permissions denied on home directory, upgrades on slow connections).

Make an actual Release to have somewhere to stick the binaries.