flow stop, servermsg out of stop, flow command modules

Summary: Move nice_kill from ClientStop command functor to param module.

Reviewed By: @jwatzman

Differential Revision: D1421357
Make hhvm print errors and abort if an HNI systemlib is broken

Summary: A parse error currently just leads to everything in the systemlib not
being defined.

Reviewed By: @ptarjan

Differential Revision: D1421895
Fix support for parse_str; treat it like extract

Summary: Assume it trashes the variable environment, and in repo mode make it
part of the DisallowDynamicVarEnvFuncs scheme.  Also close a few holes in this
stuff in fb_rename_function and simple_function_call.cpp.

Closes #3081.

Reviewed By: eletuchy, ptarjan

Differential Revision: D1422197
Remove uses of RegNumber outside X64Assembler.

Summary: Prefer Reg64 (etc) instead.

Reviewed By: @oyamauchi

Differential Revision: D1421690
Remove blocking acquire of the write-lease in smashPrologueGuards

Summary: It was only needed to unprotect the tc, which we no longer do.

Reviewed By: @swtaarrs

Differential Revision: D1424510