Tools for analyzing imports.

Provides the commands

• #redundant_imports which lists any transitively redundant imports in the current module.
• #min_imports which attempts to construct a minimal set of imports for the declarations in the current file. (Must be run at the end of the file. Tactics and macros may result in incorrect output.)
• #find_home decl suggests files higher up the import hierarchy to which decl could be moved.
• #import_diff foo bar ... computes the new transitive imports that are added to a given file when modules foo, bar, ... are added to the set of imports of the file.