Rewrote install batch file in Lua.

This is mostly a direct translation, so there are lots of things to
improve, but it is a working install script written in Lua.
Fixes by @Tieske to the installer
Fixes to the patch feature, contributed by Philipp Janda
Merge branch 'master' of github.com:keplerproject/luarocks
Improve patch compatibility, as suggested by Philipp Janda
Merge pull request #126 from ignacio/install_lua

Whoa, it does not feel like 1994 anymore!!
using objdump.exe to automatically detect the runtime dll to use for the chosen interpreter
added comment
fix: if interpreter has no runtime, check link library for runtime used.
fix; no longer check link lib when interpreter has no runtime specified, but list all dll's interpreter depends upon and check those for the runtime (1 level deep only)
Merge pull request #130 from Tieske/auto_detect_runtime

Win installer update; auto detect runtime
changed failure to detect runtime into a warning. objdump.exe does not support 64bit windows
Merge pull request #132 from Tieske/auto_detect_runtime

changed failure to detect runtime into a warning.
Avoid overwriting the current rockspec when unpacking a source .zip that happens to contain one.
(Case in point: sha2 0.2.0-1)
Support for updating versions of packages that remain with the same upstream URL, but only update their contents.
(Case in point: modules by lhf)