support for dyld shared cache

[psifertex]

See: http://iphonedevwiki.net/index.php/Dyld_shared_cache for more info.

[cornejo]

If you need to get copies of a dyld_shared_cache_ file then you can follow the steps here (http://newosxbook.com/articles/OTA.html) to extract one for yourself from one of the updates here (https://www.theiphonewiki.com/wiki/OTA_Updates)

Note that the files taken from actual phones are a) encrypted (I believe?) and b) have some form of ASLR pre-applied to them.

[psifertex]

Blocking on #133