Avoid mapscript function name warnings

[geographika]

Currently, Sphinx is reporting several of the following errors. This pull request fixes this.

WARNING: Summarised items should not include the current module. Replace 'mapscript.add_dll_path' with 'add_dll_path'. [autosummary.import_cycle]
WARNING: Summarised items should not include the current module. Replace 'mapscript.fromstring' with 'fromstring'. [autosummary.import_cycle]
WARNING: Summarised items should not include the current module. Replace 'mapscript.msCleanup' with 'msCleanup'. [autosummary.import_cycle]
WARNING: Summarised items should not include the current module. Replace 'mapscript.msConnPoolCloseUnreferenced' with 'msConnPoolCloseUnreferenced'. [autosummary.import_cycle]
WARNING: Summarised items should not include the current module. Replace 'mapscript.msFreeImage' with 'msFreeImage'. [autosummary.import_cycle]