Upgrade to Lua 5.2, but keep compatible with Lua 5.1

Done in this commit:
 - upgrade module declaration and loading:
   - "module" idioms are replaced by returning the module table
   - declare a local variable for the loaded module
   - declare private function local and export module functions through
     the module table
 - upgrade the getenv function by calling or emulating getfenv
 - export the is_test_key function to enable customization
 - suites are stored in an indexed table to run suite in the same order
   they are added. Tests are run in arbitrary order.
 - update tests and test suites files
 - bumps to version 0.9.5 and update the rockspec accordingly:
   No need to fix "lua >= 5.1" to "lua = 5.1" thanks to this upgrade.
 - update README.md

Has been tested successfully with Lua 5.1, Lua 5.2 and luajit 2.0.3.

README.md

@@ -7,8 +7,9 @@ It's largely upwardly compatible from [lunit][], with the following changes:
   not change any functions from the standard library.
 * If running tests in only one file, no module declaration is necessary.
 * For multiple suites, register them with lunatest.suite("file").
-  This uses require to load the suite, and uses the same methods to
-  match filenames with modules. (Note: should use module(...) in the file.)
+  This uses require the file suite to return a table containing the suite
+  related functions as well as the test functions. (Note: non local tests
+  functions found outside the returned table go to the main suite.)
 * It doesn't have any dependencies except Lua, though if present, it
   will use lhf's [lrandom][] module (for consistent pseudorandom numbers
   across operating systems) and [luasocket][]'s gettime() for timestamps).

lunatest-0.9.1-0.rockspec → lunatest-0.9.5-0.rockspec

@@ -1,8 +1,8 @@
 package = "lunatest"
-version = "0.9.1-0"
+version = "0.9.5-0"
 source = {
    url = "git://github.com/silentbicycle/lunatest.git",
-   tag = "v0.9.1"
+   tag = "v0.9.5"
 }
 description = {
    summary = "xUnit-style + randomized unit testing framework",
@@ -25,5 +25,5 @@ build = {
    type = "builtin",
    modules = {
       lunatest = "lunatest.lua"
-   }           
+   }
 }