gnulib-tool.py: Fixes for conditional dependencies. * pygnulib/GLModuleSystem.py (GLModule.shell_id_chars): New constant. (GLModule.getShellFunc): Don't use md5 just because of an '_' character. (GLModule.getShellVar): Likewise. (GLModule.getConditionalName): Include a newline in the md5 input. * pygnulib/constants.py (ALPHANUMERIC): Remove constant.