Add rounding modes to normal floating point arithmetic
Add Float32 rounding mode tests
Integrate the new rounding modes with BigFloats

This changes the old rounding mode sketch to a more intuitive one,
and using types instead of constants seems to be more logical.
Export RoundAwayZero too (even though it only works for BigFloats)
Stop hardcoding the `fenv.h` constants

As suggested by Viral in https://github.com/JuliaLang/julia/pull/3149
Fix bug while parsing fenv_constants.h
Renaming of the rounding modes
Fixes post-rebase
Remove fenv_constants.jl, as it is auto-generated
Documentation for the rounding modes (manual + stdlib)

It also includes some updates to some related sections about
BigFloats.
Fix issue with fenv.h and Ubuntu 12.04

If the values from fenv.h aren't found by the C preprocessor, it uses
the default ones for x86/x64
fix #4189

bug when accessing a cglobal as different types
Unexport some mmap functions
Added footnote in parallel computing chapter on MPI

The Julia manual makes the statement that Julia's parallel programming model is
unlike MPI. This is not entirely true. The current MPI standard includes
mechanisms for remote memory access; i.e. one-sided communication. Thus, users
familiar with the latest MPI standard may find the documentation confusing.

To rectify this problem, a footnote was added to clarify the meaning of the term
"MPI", as used by the Julia manual.
Merge pull request #4196 from bsilbaugh/revise-parallel-doc

Added footnote in parallel computing chapter on MPI
fix revcomp perf test for new isequal behavior
fix performance bug affecting some inner functions
possibly fix #4191
surround hidden names in __

this might as well be a convention. it also prevents a mangled version of
"foo" from tab-completing with prefixes of "foo".

exclude symbols containing '#' from tab completions; these names are not
typeable anyway.

fixes #3163
Revert "Update windows calculation of jl_cpu_cores to disregard hyperthreading"

This reverts commit 667715462041bcf9ab7f7eea428958e2c226ee32