Fix #6372

This adds the package to REQUIRE on Pkg.clone() if it exists in
METADATA. This means that calling Pkg.clone() on a repo that's on an
old tag will result in the package getting updated to the latest
release, but that seemed preferable to making Pkg.clone() on a package
that's on a tag result in a pinned package.
add jl_get_cpu_name function to libjulia

thin ccall'able wrapper around llvm::sys::getHostCPUName
Modify jl_get_cpu_name to use jl_pchar_to_string,

add Sys.cpu_name
Move cpu_name into init_sysinfo()
Evaluate and print parts of comparisons in `@test`.
Adds a resultexpr field to Failure and Success.
Add Dates module to Base
Add back llvmcall
Import update llvmcall from cxx branch
Fix build for non-MCJIT versions of Julia & Add tests
Revamp netload tests to more verbose and resiliient style
Fix nettest to run on multiple workers again
Whoops, accidentally reduced test case size
Update Package Development documentation
more explanation of abstract types

Several points concerning abstract types eluded me when I first read the manual; I have written additional paragraphs to elucidate these points.
more explanation of immutable

Some aspects of 'immutable' escaped me when I first read the manual and were clarified by Stefan Karpinski.  II think other new users might benefit from this clarification, so I put some additional paragraphs in the manual.
added a paragraph about elementwise

As far as I can see, elementwise operators are never introduced or defined in the manual, so I added a paragraph to introduce and define them.
Merge branch 'master' of https://github.com/JuliaLang/julia into jq/dates
Add missing millisecond to month/year-TimeType arithmetic
Cleanup some definitions for Period types. Removes redundants and adds a few math operations
Add internal conversion methods to Day and Millisecond. This builds a foundation for better range support