Rename copy_unsafe! to unsafe_copy! and export it (#2871).

Also add a version of unsafe_copy! that works with pointers,
and acts as a memcpy wrapper.

I have not added this to the list of deprecations since the function
was not exported until now.
Fix typo: export unsafe_copy!
Documents using Travis CI for packages
fix #2905 - regression caused by 0228c1cab0222fc4684954842fd6e028601fc1ba re: AST compression efficiency
fix #2904, add definition of pointer_to_array with single integer dimension argument
pkg2 wip: determine fixed packages by reachability from METADATA.

The idea here is that once a package commit is included in a version
that makes it into METADATA, you no longer need to stay on version
since it's been included upstream. The workflow here is that someone
makes a fix locally, submits it for upstream inclusion, meanwhile
the package is off-branch but with local changes, therefore fixed.
Once the fix gets included upstream and published to a version in
METADATA, it's safe to start managing the package again, so it is no
longer fixed.

In far less complicated cases, this is effective for the situation
where a package was on an off-branch commit that is no longer a
known version in METADATA but was an ancestor of one, such as when
0.0.0 is overwritten or when an older published version is "retired"
and no longer considered a candidate for installation.
add !== operator, meaning !(a===b)
pkg2 wip: get requirements from METADATA when clean and konwn.