Add CFLAGS='-march=native -O3' when compiling ruby

This flags were selected after reading Andrei Lisnic's post _[Making your ruby fly](http://alisnic.net/blog/making-your-ruby-fly/)_.

Initial benchmarks show some minimal performance improvements when running a simple benchmark that performs:

* recursive calculation of n-th Fibonacci number;
* creation and writing to several temp files.

This is the [benchmark script](https://gist.github.com/4181899#file_thebench.rb):

```ruby
require "benchmark"
require "tempfile"

def fib n
  case n
  when 0 then 0
  when 1 then 1
  else
    fib(n-1) + fib(n-2)
  end
end

n = (ARGV[0] || 10).to_i
t = (ARGV[1] || 1000).to_i

Benchmark.bmbm(20) do |r|
  r.report("fib(#{n})") { fib(n) }
  r.report("#{t} tempfiles") do
    t.times do |i|
      tmp = Tempfile.new("bench")
      begin
        tmp.write i
      rescue
      ensure
        tmp.close
        tmp.unlink
      end
    end
  end
end

puts
```

When running the script with the latest ruby from homebrew, I've got the following results:

```
>> /usr/bin/time -l ruby thebench.rb 30 1000
Rehearsal --------------------------------------------------------
fib(30)                0.260000   0.000000   0.260000 (  0.255475)
1000 tempfiles         0.120000   0.250000   0.370000 (  0.429621)
----------------------------------------------- total: 0.630000sec

                           user     system      total        real
fib(30)                0.260000   0.000000   0.260000 (  0.259108)
1000 tempfiles         0.130000   0.270000   0.400000 (  0.848950)

        1.85 real         0.79 user         0.52 sys
   7073792  maximum resident set size
         0  average shared memory size
         0  average unshared data size
         0  average unshared stack size
      1743  page reclaims
         0  page faults
         0  swaps
        42  block input operations
        85  block output operations
         0  messages sent
         0  messages received
         0  signals received
        65  voluntary context switches
      1893  involuntary context switches
```

Running the script with a customized version with `CFLAGS="-march=native -O3"` the results are the following:

```
>> /usr/bin/time -l bin/ruby thebench.rb 30 1000
Rehearsal --------------------------------------------------------
fib(30)                0.260000   0.000000   0.260000 (  0.255356)
1000 tempfiles         0.120000   0.250000   0.370000 (  0.457608)
----------------------------------------------- total: 0.630000sec

                           user     system      total        real
fib(30)                0.260000   0.000000   0.260000 (  0.256357)
1000 tempfiles         0.120000   0.250000   0.370000 (  0.433369)

        1.44 real         0.79 user         0.50 sys
   7438336  maximum resident set size
         0  average shared memory size
         0  average unshared data size
         0  average unshared stack size
      1832  page reclaims
         0  page faults
         0  swaps
         3  block input operations
        71  block output operations
         0  messages sent
         0  messages received
         0  signals received
        33  voluntary context switches
      1892  involuntary context switches
```

As these benchmarks aren't real use cases I tested against a test suite in a medium sized project, with the following results for default ruby:

```
>> /usr/bin/time -l rake test
280 tests, 994 assertions (280 passed, 0 pending, 0 failed, 0 errored)
Ran in 11.013013 seconds

       13.89 real        10.85 user         0.81 sys
  51933184  maximum resident set size
         0  average shared memory size
         0  average unshared data size
         0  average unshared stack size
     12864  page reclaims
        78  page faults
         0  swaps
        11  block input operations
       107  block output operations
     39957  messages sent
     28111  messages received
         0  signals received
      1193  voluntary context switches
       242  involuntary context switches
```

And optimized ruby:

```
>> /usr/bin/time -l ~/dev/tmp/homebrew/bin/rake test
280 tests, 994 assertions (280 passed, 0 pending, 0 failed, 0 errored)
Ran in 10.628247 seconds
Coverage report generated for Protest to /Users/inkel/dev/citrusbyte/bleuacre/coverage. 1278 / 1686 LOC (75.8%) covered.
       11.89 real        10.73 user         0.79 sys
  49840128  maximum resident set size
         0  average shared memory size
         0  average unshared data size
         0  average unshared stack size
     12267  page reclaims
       154  page faults
         0  swaps
         2  block input operations
        31  block output operations
     39955  messages sent
     28099  messages received
         0  signals received
      1090  voluntary context switches
       203  involuntary context switches
```

Benchmark results are also shared in a [public gist](https://gist.github.com/4181899).

As you can see this results are hardly conclusive of any performance improvements introduced by using those custom CFLAGS, so I'd like to know if somebody else can contribute with benchmarks results, and if there's interest with this pull request I might try and add the falcon patch.

Hope you find this useful.