Adding fdopen workaround and fstat fix to nacl_io.

fdopen in glibc normally fails because fcntl is called inside glibc's
implementation (which doesn't have a hook).
Implementing fdopen in terms of fopencookie.

Modifying the http mount to set the file type to indicate a regular file.

R=binji@chromium.org, sbc@chromium.org
BUG=https://code.google.com/p/nativeclient/issues/detail?id=3362
TEST=None

Review URL: https://codereview.chromium.org/23983020

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225027 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 225027