Compatibility: Try bob.sh and then bob.rb if bob (binary) fails

[jacob-carlborg]

The pre-built "bob" tool that comes with Tango to build Tango has two (very familiar) problems on older systems:

• Fails with Invalid instruction (Tango Issue #2061) on systems without SSE2 (such as all 32-bit AMD Athlons)
• It's built on a newer OS and therefore requires a newer glibc/OS (yea, just what we've already been through before with DVM itself)

But, Tango also has two alternate versions of bob: build/script/bob.sh (which requires bash :/ ) and build/script/bob.rb (which requires ruby :/ ). Obviously they all have their potential compatibility downsides, so I'm thinking that if the binary "bob" fails, then maybe DVM should then try "bob.sh", and then "bob.rb" as a last resort.

Reference: dvm/issue/17/compatibility-try-bobsh-and-then-bobrb-if