Add the ability to disable deprecation warnings with a cmd line switch

The `--depwarn={yes|no}` flag turns on/off method warnings and deprecated syntax warnings
in the parser.

(unexported) `compileropts()` method added to retrieve the
compileropts struct from libjulia.

(unexported) `syntax_deprecation_warnings(::Bool)` method added to
turn off syntax deprecation warnings in the parser at runtime.
the method returns the previous syntax deprecation warning state.

add NEWS entry and update docs for command line switches
Fix #9366, save_stack causing win64 test failures when inlined
Fix #9103, implementing `cd -` in REPL shell mode
repl_cmd() prints to the repl's output stream

(not STDOUT)
tests for repl shell mode cd feature
fix long string warning in repl shell mode tests
Mention rebinding behavior of +=

Explicitly mention "rebind", hopefully facilitates search
Ref: https://groups.google.com/d/msg/julia-users/ujxesTieDHU/zWrZNAUHelkJ
Use language: julia in default .travis.yml

and add the os: section for mac testing (has to be explicitly enabled
by sending an email to support@travis-ci.com, see
http://docs.travis-ci.com/user/multi-os )
add git fetch --unshallow in commented out script section

add explanatory comment
turn on coverage in commented-out script section
get versioninfo() from AppVeyor

[ci skip]
Really fix #9366

pass a stack-copy of ctxThread in jl_throw_in_ctx to rec_backtrace_ctx
trim the stack back down to the bare necessity
run win64 in parallel again on appveyor

let's see if maybe we just fixed the cause of the freezes
[ci skip]
explain resize! behavior; fixes #9313
Make `Pkg.build` error message clearer.
fix #7395, and copy just the useful parts of CONTEXT in jl_throw_in_ctx, before rec_backtrace_ctx destroys the recorded stack pointer
Update networking-and-streams.rst

`read(stream, array)` is deprecated in favor of read!()
fix 32 bit oops from ed5a8fcb93
REPL: passthru ctrl-arrow keys