make import/using .Foo do a relative search for Foo, and the old syntax search from Main (the top level).
addresses #2375

this is quite disruptive, but I think I prefer it. after all, most of
the imports in Base are of internal modules, so they should be marked as
such.
Merge branch 'master' of github.com:JuliaLang/julia into jb/relativeimport
make relative imports explicit based on the number of leading dots
fix #2780
Merge branch 'master' of github.com:JuliaLang/julia
Introduce USE_SYSTEM_RMATH to allow for system-packaged Rmath
Add in Rmath to travis config
fix #2781, ensure that the task that handles an error actually has an active handler
fix #2778, improve dataflow of finally blocks
fix #2779, chained comparisons doc
move collect() to general collections section
a couple doc fixes related to immutability
document immutable types. closes #2565
Merge pull request #2783 from staticfloat/usesystemrmath

Introduce USE_SYSTEM_RMATH to allow for system-packaged Rmath
fix #2784
make both dividing by zero and overflowed int division give an error, fixes #355
rename DivideByZeroError to DivideError, which reflects the fact that more
than one thing can go wrong, and is also shorter.
this is designed to match CPUs that raise an FPE in both cases.
intercept repeated show(lasterr) errors, a case that usually means something deep in the system is broken
for #2787
remove some old files, closes #2743
a trivial formatting change
Update CONTRIBUTING.md
Updates package contribution instructions

- Adds instructions to migrate development from master to devel branch
- Adds comments for all but the most basic git commands
- Adds caution reminding developers to be familiar with git and seek help when it breaks
- Tells user to delete custom branch after submission to METADATA is accepted.

Minor structural changes and reorganizations, e.g. base doc page now has link to Chinese Julia manual in Chinese.
Get package developer to move onto new working branch ASAP.
Ensure branch point is from devel