Add and fix sharing specs for Range#{cover?,include?,member?,===}
Fix Range#{include?,member?} for X19

It should basically depend element.succ from X19.
And old behavior is keeping by Range#cover?.

Example
-------

    ('a'..'c').include? 'bc'

Results
-------

* MRI 1.8.7    #=> true
* MRI 1.9.3    #=> false
* Rubinius X18 #=> true
* Rubinius X19 #=> true  #Fix here
Add specs on Numeric#step called as ±inf.step(±inf, ±step).
Numeric#step: stop if err is not finite.
Add IO slot for path since File uses it often

This makes accessing @path faster for File.
Guard memory allocations for JIT memory with spinlock

This fixes a crash issue where the JIT was running independent from the
GC and the GC was deallocating JIT memory at the same time. We don't
want to make the whole JIT generation GC dependent, since that causes
performance issues, so we guard all memory allocations here with a
spinlock.

The crash would be exposed with these backtraces where things were
modified concurrently:

Thread 6 (process 70553):
 #0  rubinius::jit::FreeRangeHeader::AddToFreeList () at /Users/dirkjan/Code/rubinius/vm/llvm/jit_memory_manager.hpp:151
 #1  0x000000010989f037 in rubinius::jit::MemoryRangeHeader::TrimAllocationToSize (this=0x10f7ec688, FreeList=0x10f7ec688, NewSize=5064) at vm/llvm/jit_memory_manager.cpp:211
 #2  0x000000010989bb75 in rubinius::jit::RubiniusRequestJITMemoryManager::endFunctionBody (this=<value temporarily unavailable, due to optimizations>, F=<value temporarily unavailable, due to optimizations>, FunctionStart=<value temporarily unavailable, due to optimizations>, FunctionEnd=0x13c8 <Address 0x13c8 out of bounds>) at jit_memory_manager.hpp:317
 #3  0x0000000109b4f852 in (anonymous namespace)::JITEmitter::finishFunction ()
 #4  0x0000000109946106 in (anonymous namespace)::Emitter<llvm::JITCodeEmitter>::runOnMachineFunction ()
 #5  0x0000000109bbbc30 in llvm::MachineFunctionPass::runOnFunction ()
 #6  0x0000000109f1beb2 in llvm::FPPassManager::runOnFunction ()
 #7  0x0000000109f1b9f9 in llvm::FunctionPassManagerImpl::run ()
 #8  0x0000000109f1b8a1 in llvm::FunctionPassManager::run ()
 #9  0x0000000109b461ab in llvm::JIT::runJITOnFunctionUnlocked ()
 #10 0x0000000109b46148 in llvm::JIT::runJITOnFunction ()
 #11 0x0000000109898fcc in rubinius::jit::Compiler::generate_function (this=0x10d485d38, indy=true) at vm/llvm/jit_compiler.cpp:118
 #12 0x00000001098ada93 in rubinius::BackgroundCompilerThread::perform (this=0x7fce81633240) at vm/llvm/state.cpp:345
 #13 0x00000001098ad4ef in rubinius::utilities::thread::Thread::delete_on_exit () at /Users/dirkjan/Code/rubinius/vm/util/thread.hpp:79
 #14 0x00000001098ad4ef in rubinius::utilities::thread::Thread::trampoline (arg=0x7fce81633240) at thread.hpp:211
 #15 0x00007fff8e73c7a2 in _pthread_start ()
 #16 0x00007fff8e7291e1 in thread_start ()

Thread 5 (process 70553):
 #0  0x00007fff952b5386 in __semwait_signal ()
 #1  0x00007fff8e7c6800 in nanosleep ()
 #2  0x00007fff8e7c668a in sleep ()
 #3  0x000000010969c9dd in rubinius::segv_handler (sig=11) at vm/environment.cpp:211
 #4  <signal handler called>
 #5  rubinius::jit::FreeRangeHeader::AddToFreeList () at /Users/dirkjan/Code/rubinius/vm/llvm/jit_memory_manager.hpp:151
 #6  0x000000010989ee53 in rubinius::jit::MemoryRangeHeader::FreeBlock (this=0x10f7c88f0, FreeList=<value temporarily unavailable, due to optimizations>) at jit_memory_manager.hpp:155
 #7  0x00000001098ac3e7 in rubinius::LLVMState::remove (this=<value temporarily unavailable, due to optimizations>, func=<value temporarily unavailable, due to optimizations>) at jit_memory_manager.hpp:426
 #8  0x000000010983dde9 in rubinius::CodeManager::sweep (this=0x7fce8180a2d8) at vm/gc/code_manager.cpp:107
 #9  0x0000000109750e7e in rubinius::ObjectMemory::mark () at /Users/dirkjan/Code/rubinius/vm/objectmemory.hpp:634
 #10 0x0000000109750e7e in rubinius::ObjectMemory::collect_mature_finish (this=0x7fce8180a200, state=0x10c94fec8, data=0x7fce8528b220) at vm/objectmemory.cpp:636
 #11 0x0000000109843d8a in rubinius::State::memory () at /Users/dirkjan/Code/rubinius/vm/state.hpp:171
 #12 0x0000000109843d8a in rubinius::ImmixMarker::perform (this=0x7fce8163a720, state=0x10c94fec8) at vm/gc/immix_marker.cpp:172
 #13 0x0000000109843b71 in rubinius::immix_marker_tramp (state=0x10f7ec688) at vm/gc/immix_marker.cpp:18
 #14 0x00000001098094c0 in rubinius::Thread::in_new_thread (ptr=0x7fce86a23e70) at vm/builtin/thread.cpp:250
 #15 0x00007fff8e73c7a2 in _pthread_start ()
 #16 0x00007fff8e7291e1 in thread_start ()
Add basic instructions for security reports

We also need to add a page to the website with the policy and links to
the public key etc.

Related to #2417
Use >= for mtime comparison for quick recompile

We might rebuild the same file within a very short time frame, in that
case we would run the old compiled cache which would be incorrect.

Fixes #2430
Allow linking against a shared libLLVM
Merge pull request #2434 from heftig/master

 Allow linking against a shared libLLVM
Merge pull request #2426 from razielgn/feature-numeric-step-infinity-combinations

Numeric#step called as ±inf.step(±inf, ±step)
Merge pull request #2416 from kachick/fix-range-include-x19

Range#{include?,member?} should basically depend element.succ from X19
Add a spec for Module#public when given an undefined name

`raise_error(NameError)` matches NoMethodError too.
Add a spec for Module#protected when given an undefined name
Add a spec for Module#private when given an undefined name
Add a spec for main.public when given an undefined name
Add a spec for main.private when given an undefined name
Fix specs for Module#public_class_method when given an undefined name
Fix specs for Module#private_class_method when given an undefined name
Fix exceptions when visibility setters given an undefined name

* Module#{public,protected,private}
* Module#{public,private}_class_method
* main.{public,private}