Use vm.isContext() to properly identify contexts.

PR-URL: nodejs/node-v0.x-archive#25382
PR-URL: io.js PR-URL here
Reviewed-By: Colin Ihrig <[email protected]>

Fix the regexp used to detect 'Unexpected token' errors so that they can
be considered as recoverable. This fixes the following use case:

> var foo = 'bar \
... baz';
undefined
> foo
'bar baz'
>

Fixes: nodejs/node-v0.x-archive#8874
PR-URL: nodejs/node-v0.x-archive#8875
PR-URL: insert io.js PR-URL
Reviewed-By: Colin Ihrig <[email protected]>

test-repl-tab-complete.js contains numerous assertions that are
never run. Anything that results in a ReferenceError bails out,
and never calls the functions containing the assertions. This
commit adds checking for successful tab completions, as well as
ReferenceErrors.

PR-URL: insert here