Updated info in README.md

* CentOS 5 building with gcc44
* Ubuntu PPAs
* Troubleshooting table
* Removed Rmath reference
Fixes ssh tunnel command setup. Also fixes #3671
sorting: make `order` and `alg` keyword arguments.

The idea here is that the ordering and algorithm for sorting are
two orthogonal parameters that have sensible defaults: neither,
both or either can be independently specified. The resulting API
is slightly more verbose but also somewhat more self-documenting.

Another sign that this might be on the right track is that this
change reduces the LOC of base/sort.jl by 41 lines and reduces the
method count of sort, for example, from 12 to 6.
sorting: move matrix sorts up with other generic sorting functions.
sorting: eliminate a few nans2{left,right} definitions via defaults.
sorting: keyword arguments for `by` and `lt` as well.
document SymTridiagonal, improve other tridiagonal docs
sorting: make ReverseOrder parametric -- can reverse any ordering.
more helpful error messages in ccall and cglobal
cleanup UV objects, especially status codes. fixes #1923. fixes #3676
on uv close, notify all waiting tasks
fix @assert for use during sysimg build, and use it
fix #3544
fix small TODO in quadgk (use SymTridiagonal eigensolver)
Fail earlier if FD is already being watched
Merge pull request #3677 from kmsquire/readme_updates

Updated info in README.md
fix serious codegen bug in struct construction
fix deprecation of start_timer
Merge branch 'master' of github.com:JuliaLang/julia
fix #1768
sorting: add `rev` boolean keyword to reverse any sort ordering.

Also added lt, by, order, rev keywords to the searchsorted* funcs.