[perf] disabling _populateCache() in loader in favor of an on-demand process to create internal module info based on the raw meta when the module is needed

Initial analysis:
---------------------

For a very basic page with all necessary modules in the page upfront, and a YUI().use(‘json-stringify’) call, will run under 20ms in chrome/desktop, but it takes more than 100ms in safari iPad3.

For a more complex example, adding more modules (app level modules), we can clearly see more degradation of the initialization, even though none of those modules are "used". Here is an example using modules from screen.yahoo.com (almost 400 new modules + the 407 modules from yui core):

http://jsbin.com/iPOriSAS/1/edit

For what we can see in the profiling, _populateCache(), which is executed once per Y instance, it will do a one time operation to digest all the raw metadata from YUI.Env.modules, passing them thru addModule() method that will do a basic expansion of the meta without doing the recursive computation to expand the dependencies, that happens on demand.

By using the loader built of this branch, we seed a good deal of improvement, and overall a constant time to use despited the number of extra modules added thru the metas, which is exactly what we are looking for. 

Changes:
--------------

Loader keeps a member called `moduleInfo`, which is a hash with the internal meta for every module. This structure is used within the loader and from yui.js as well. This PR is proposing a shim on top of that structure to se can populate the cache for each individual module from the raw meta structure `YUI.Env.modules` when we needed. This will help to not have to walk thousand of modules as part of the initialization of the first YUI instance.

A quirk on this new way of initialization is that conditional modules are not requested by any other module in the require chain, which means they will have to be analyzed before applying any operation to compute dependencies, for that, we are just warming up the conditional cache (which is normally 16 entries for yui core), instead of just initializing all core modules (400+).

Performance tests
-------------------------

command: `yb src/loader/tests/performance/loader-tests.js --phantom --ref v3.14.1 --ref v3.15.0`

### loader resolve core modules
	┌───────────┬───────────────────────────┬───────────────────────────────────┬───────────────────────────┐
	│           │  Safari (7.0.1) / Mac OS  │  Chrome (33.0.1750.117) / Mac OS  │  Firefox (27.0) / Mac OS  │
	├───────────┼───────────────────────────┼───────────────────────────────────┼───────────────────────────┤
	│  v3.14.1  │  44.788  ±3.7%            │  44.546  ±3.8%                    │  21.736  ±4.6%            │
	│  Working  │  189.414  ±4.4%  +323%    │  127.738  ±8.9%  +187%            │  86.822  ±3.8%  +299%     │
	│  v3.15.0  │  157.768  ±3.9%  +252%    │  109.642  ±4.7%  +146%            │  80.497  ±3.9%  +270%     │
	└───────────┴───────────────────────────┴───────────────────────────────────┴───────────────────────────┘

### loader resolve application modules
	┌───────────┬───────────────────────────┬───────────────────────────────────┬───────────────────────────┐
	│           │  Safari (7.0.1) / Mac OS  │  Chrome (33.0.1750.117) / Mac OS  │  Firefox (27.0) / Mac OS  │
	├───────────┼───────────────────────────┼───────────────────────────────────┼───────────────────────────┤
	│  v3.14.1  │  595.568  ±5.7%           │  245.833  ±7.7%                   │  231.745  ±5.0%           │
	│  Working  │  6.721k  ±3.3%  +1029%    │  3.450k  ±7.1%  +1304%            │  2.500k  ±4.3%  +979%     │
	│  v3.15.0  │  696.895  ±3.0%  +17%     │  279.307  ±4.9%  +14%             │  260.851  ±3.8%  +13%     │
	└───────────┴───────────────────────────┴───────────────────────────────────┴───────────────────────────┘

### caculate dependecies
	┌───────────┬───────────────────────────┬───────────────────────────────────┬───────────────────────────┐
	│           │  Safari (7.0.1) / Mac OS  │  Chrome (33.0.1750.117) / Mac OS  │  Firefox (27.0) / Mac OS  │
	├───────────┼───────────────────────────┼───────────────────────────────────┼───────────────────────────┤
	│  v3.14.1  │  87.696  ±3.8%            │  78.881  ±4.2%                    │  44.247  ±4.4%            │
	│  Working  │  306.211  ±3.0%  +249%    │  217.144  ±8.9%  +175%            │  154.839  ±3.1%  +250%    │
	│  v3.15.0  │  224.967  ±2.7%  +157%    │  132.550  ±7.0%  +68%             │  110.696  ±3.9%  +150%    │
	└───────────┴───────────────────────────┴───────────────────────────────────┴───────────────────────────┘

### loader constructor with global cache
	┌───────────┬───────────────────────────┬───────────────────────────────────┬───────────────────────────┐
	│           │  Safari (7.0.1) / Mac OS  │  Chrome (33.0.1750.117) / Mac OS  │  Firefox (27.0) / Mac OS  │
	├───────────┼───────────────────────────┼───────────────────────────────────┼───────────────────────────┤
	│  v3.14.1  │  1.159k  ±4.6%            │  402.577  ±4.5%                   │  419.501  ±4.0%           │
	│  Working  │  35.813k  ±3.5%  +2990%   │  9.923k  ±7.8%  +2365%            │  12.131k  ±3.6%  +2792%   │
	│  v3.15.0  │  1.203k  ±3.0%  +4%       │  406.346  ±4.1%  +1%              │  435.124  ±3.6%  +4%      │
	└───────────┴───────────────────────────┴───────────────────────────────────┴───────────────────────────┘

### loader constructor without cache
	┌───────────┬───────────────────────────┬───────────────────────────────────┬───────────────────────────┐
	│           │  Safari (7.0.1) / Mac OS  │  Chrome (33.0.1750.117) / Mac OS  │  Firefox (27.0) / Mac OS  │
	├───────────┼───────────────────────────┼───────────────────────────────────┼───────────────────────────┤
	│  v3.14.1  │  143.610  ±8.3%           │  127.687  ±5.7%                   │  95.255  ±7.2%            │
	│  Working  │  4.830k  ±2.9%  +3263%    │  3.451k  ±12.1%  +2603%           │  2.972k  ±3.7%  +3020%    │
	│  v3.15.0  │  138.078  ±8.1%  -4%      │  135.419  ±6.8%  +6%              │  91.891  ±5.6%  -4%       │
	└───────────┴───────────────────────────┴───────────────────────────────────┴───────────────────────────┘