Add PkgResolve module, use it in Pkg

Substitutes the linear programming approach to
package resolution with a max-sum algorithm
PkgResolve: prune unnecessary versions
PkgResolve: misc. improvements

*) fields no longer normalized
*) accuracy settable via environment variable
*) better handling of unsat cases
Fix: position() after skip() did not report correct position.
Update Travis to use llvm-3.2
Merge pull request #2003 from staticfloat/travisllvm32

Upgrade Travis to use llvm-3.2
re-fix SuiteSparse tests on mac & linux (replace a build-only flag
incorrectly removed during $(USR) -> $(BUILD) update)
fix USE_SYSTEM_GLPK and glpk target. fixes #2004
fix location of launch-julia-webserver.bat to be in webserver directory
Merge pull request #2001 from GunnarFarneback/ios

Fix: position() after skip() did not report correct position.
Make documentation examples current.
add importall. for #2002.
More documentation updates.
Merge branch 'master' of github.com:JuliaLang/julia
fix Pkg usage of cwd() and add deprecation of cwd() for pwd().

Closes #2007.
Print warnings to stderr.
Remove potential features from the manual
Merge branch 'master' of github.com:JuliaLang/julia
Merge pull request #2009 from dcjones/master

Print warnings to stderr.
base/path.jl: shorten _regex suffixes to _re.