Merge branch 'hotfix/1.20.9'
add extra warning for apt-get update 404 / 100 error, closes #1901
fix displaing green "Using:" in generated rvmrc files, fix #1903
make sure proper version of autoconf is installed for ruby-head, fix #1908
add jruby-1.7.4
SECURITY: do not allow PATH separator in gemset names, thanks to @DavidEGrayson
1.20.10
Merge branch 'master' into hotfix/1.20.10
Merge branch 'hotfix/1.20.10' into stable