Expose CWD and import search paths in GHCi via new `:show paths` command

• Currently, GHCi provides a :cd command but no respective builtin command to query the currently set path.
• Moreover, there's no obvious way to query the currently active importPaths dynamic flags field, to find out which -i options are currently in effect.

The attached patch extends :show with a :show paths subcommand, printing the CWD and the current value of importPaths:

Ok, modules loaded: Main, InteractiveUI, Paths_ghci_ng, GhciMonad, GhciTags.
λ> :show paths 
current working directory: 
  /home/hvr/Haskell/My/ghci-ng
module import search paths:
  dist/build/ghci-ng/ghci-ng-tmp
  ghc
  dist/build/autogen

λ> :set -i

λ> :show paths 
current working directory: 
  /home/hvr/Haskell/My/ghci-ng
module import search paths: none

> :cd /tmp
Warning: changing directory causes all loaded modules to be unloaded,
because the search path has changed.

> :show paths 
current working directory: 
  /tmp
module import search paths: none

Trac metadata

Trac field	Value
Version	7.7
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	GHCi
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