Simplify build by removing GC tweaking logic

Mono 3.0.x was the first version when Mono's SGEN GC could be
considered stable, and F# was using it by default for this
version.

But then Mono 3.2.0 was released, which defaults to SGEN GC
anyway, so there's no need to tweak F# build or scripts anymore,
as we can simplify all this by just making F# use what the
underlying mono uses as default.

If some user is interested in using SGEN GC, she should just
make sure that she's using Mono 3.2.x or higher, or just adjust
MONO_ENV_OPTIONS env var herself.
Merge pull request #247 from 7sharp9/xplat-tests

Xplat tests
Merge pull request #235 from knocte/simplify_build

Simplify build by removing GC tweaking logic
strong name dlls
Merge branch 'master' of https://github.com/fsharp/fsharp
Small changes to README.md
Remove prepositions, update name
Format corrections, correct name
Update continuous integration section
Fix text break, add link for NUnit
Correct markdown link
Shorten title, correct section case
Merge pull request #258 from brodyberg/edit_readme

Edits to README.md
update signed dlls
configure: stop allowing Mono 2.9, recommend Mono 3.2

F# 3.1 build is xbuild-based, so configure needs to check that
Mono 3.0 (or newer) is in place, not 2.9 (this old version
had limitations that prevented F# projects to build with xbuild).

We take advantage of this opportunity to re-use the AC_MSG_WARN
that recommends a mono version, to advice about using Mono 3.2
(instead of 3.0) as it defaults to SGen GC.

(Should fix #264)
Merge pull request #265 from knocte/master

configure: stop allowing Mono 2.9, recommend Mono 3.2
Merge github.com:fsharp/fsharp