Adapt to change in GHC package db flags.

GHC and ghc-pkg package db flags changed from '*-package-conf' to
'*-package-db' in 7.5.  This commit follows the change and introduces a
version check whenever those flags are used.
Merge pull request #6 from pcapriotti/master

Adapt to package-conf -> package-db change
Fix cabal-install build.
Merge pull request #7 from pcapriotti/master

Fix cabal-install build.
Don't use stdcall on Win64: It isn't supported; ccall is used instead
Define *_HOST_OS and *_HOST_ARCH variables when defining __GLASGOW_HASKELL__

In particular, this fixes building haskeline with its windows_cconv.h
header.
Maintain info about manual flags in modular solver.
Store manual flag info in search tree.
Make modular solver handle manual flags properly.
Remove goal choice nodes after reordering is completed.

This saves a lot of heap space while exploring the tree and backtracking.
Force the log for the error to be printed in parallel with the complete trace.

This saves a bit of heap space when running the solver with unlimited
backtracking enabled.
Extended a comment.
Fix warnings.
Ignore the cabal-dev dir in .gitignore.
Follow Win64 changes in GHC
Follow changes in base
Spelling.
80-col violation.
Fix warnings.
Redundant imports.