Benchmark tweaks:

* Added pi_sum_vec to Matlab, Julia and R (disabled)
* Tweaked parseint in perf.R
* Added perf.lua by Francesco Abatte (Needs the GSL Shell)
perf: Lua corrections and pi_sum_vec in Python (disabled)
perf.lua: fix oversight
perf.R: cache the pi_sum_vec range to match other implementations.
perf.lua: Adding pure Lua variants.
perf.lua: Removed pure Lua variants

... since the GSL and Julia use the same PRNG, and LuaJIT does not.
extras/pkg.jl: stub that errors if you require("pkg") [fix #2376].
Fix #2377: corrected definition of sortby(v,by,alg).
Make all numbers iterable and fix #2369 [max(Inf) hangs].
doc: update {l,r}strip and helpdb.jl
Merge pull request #2278 from pygy/PerfTests

RFC: Benchmark tweaks
Merge branch 'master' of github.com:JuliaLang/julia into jb/immutable
misc changes for immutable types, updating comments, adding keyword
feature-complete compiler support for immutable aggregates
add immutable keyword in frontend, and fix lowering of new() for it
codegen support for unboxed aggregates