make Nothing immutable
fix incorrect ccall signatures of memset, jl_readBuffer,
jl_uv_fs_t_ptr_offset, and memchr, as identified in #2901
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.
pkg2 wip: include julia as a fixed installed "package".
pkg2 wip: provide proxy version numbers for fixed packages.

These proxy versions are necessary for making fixed packages work
properly with version requirements since one has to have a version
for each fixed package against which to evaluate the feasability of
constraints on that package's version to eliminate versions of free
pacakges that won't work with the installed fixed version.
pkg2 wip: on second thought don't let dirtiness affect proxy versions.
add Cwchar_t and update docs. closes #2907
Merge branch 'master' of github.com:JuliaLang/julia
small codegen improvement in is() (use a gc root less often)
pkg2 wip: rename version_number => installed_version.
Values returned by solve methods should match type of rhs

`solve` methods involving a `CholmodFactor` object, whether called
directly or indirectly through methods for `\`, `Ac_div_B`, etc. now
return the same type of object as the right hand side.  If the rhs is
an `Array` they return an `Array`.  Previously these methods returned
a `CholmodDense` or `CholmodSparse` object.
restore commit info to VERSION (and also fix #2912)
test: add tests for version.jl

Follow-up to #2912.