faster readcsv. fixes #3350

Changes to `readdlm` for speed improvements. Instead of `readline` and `split` the new method instead slurps the whole file into memory, parses it linearly for delimiter offsets and uses `SubString` wherever possible.


With this patch:
````
               _
   _       _ _(_)_     |  A fresh approach to technical computing
  (_)     | (_) (_)    |  Documentation: http://docs.julialang.org
   _ _   _| |_  __ _   |  Type "help()" to list help topics
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 0.2.0-2039.r3771bf24.dirty
 _/ |\__'_|_|_|\__'_|  |  Commit 3771bf244d 2013-06-17 22:15:40*
|__/                   |  x86_64-apple-darwin12.4.0

julia> @time s = readcsv("vList.csv")
elapsed time: 16.183337526 seconds
1608716x9 Any Array:
   1.0  166.0  "Govindarajanagar  "  "RDU3444981"  "Mahesh B"                                            "Basavaraju"                 " ..."                     22.0   "M"
   2.0  166.0  "Govindarajanagar "    "RDU3524188"  "Kemparaju"                                           "Chikkanachari"              " ."                       34.0   "M"
````


Prior to this patch:
````
               _
   _       _ _(_)_     |  A fresh approach to technical computing
  (_)     | (_) (_)    |  Documentation: http://docs.julialang.org
   _ _   _| |_  __ _   |  Type "help()" to list help topics
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 0.2.0-2030.rbf13c7aa
 _/ |\__'_|_|_|\__'_|  |  Commit bf13c7aaf5 2013-06-16 04:52:40
|__/                   |  x86_64-apple-darwin12.4.0

julia> @time s = readcsv("vList.csv")
elapsed time: 151.918892449 seconds
1608716x9 Any Array:
   1.0  166.0  "Govindarajanagar  "  "RDU3444981"  "Mahesh B"                                            "Basavaraju"                 " ..."                     22.0   "M"
   2.0  166.0  "Govindarajanagar "    "RDU3524188"  "Kemparaju"                                           "Chikkanachari"              " ."                       34.0   "M"
````