add ISC license
add ISC license to cabal init
add data-dir to InstalledPackageInfo

the datadir location for the inplace InstallDirs was pointing to the top directory
of the package instead of the directory containing the data. this has been fixed.
since templates have already been expanded at this point, datasubdir raises an
exception an cannot be used in generalInstalledPackageInfo. therefore the
full path is stored in datadir.
Merge pull request #2233 from vincenthz/master

add ISC license
Merge pull request #2235 from luite/master

add data-dir to InstalledPackageInfo
Preliminary support for compiling signature files, using --instantiate-with.

There's no chrome here, but some of the guts for Cabal supporting compiling
signatures.  The key UI is a new --instantiate-with flag for ./Setup (no support
cabal-install side!) which properly modifies the package key, calculates extra
hole dependencies for a package, and ensures an appropriately
translated -sig-of is passed to GHC.  The UI here is supremely user-unfriendly:
the intent is that users will use cabal-install to calculate these parameters
for them.

ToDo: Cabal's inconsistency check in ./Setup needs to be adjusted to be
less zealous.

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>