use File::PATH_SEPARATOR when applicable
remove Autoproj.find_in_path

Autobuild now has a version of it, and it was unused in the
autoproj codebase
osdeps: use primarily /etc/os-release to autodetect the OS
osdeps: fix nonsensical and non-portable test for lsb_release
install rubygems-integration on ubuntu as well

Note that 12.04 does not have it, so add a special case for this
version
osdeps: *_home method call in gem and pip interaction prompts
remove duplicate character classes in regexp
don't refer to the global Autoproj.manifest in PackageSet

PackageSet has an attribute referring to its manifest, so use
it instead.
osdeps: fix test of the gem manager

The gem command is now called with RUBY -S in front, which broke the
related tests.
remove obsolete test/test_debian
test: update test for Manifest#each_package_set

The manifest used in the test was using a long-broken feature
of autoproj (shorthand notation for repositories), and was using
the 'local' package set name, which is reserved
remove unused variable
test: update test