We have had shell functions in ltmain.in for a few years without

We have had shell functions in ltmain.in for a few years without
complaint now, and recently a few more have crept in.  Make a
start at refactoring the code with shell functions, and
standardising on option parsing style:

* config/ltmain.in (func_echo, func_verbose, func_error)
(func_fatal_error, func_fatal_help, func_missing_arg)
(func_version, func_usage, func_help): Boiler plate shell
functions mostly copied from libtoolize.in.  Changed *lots* of
shell snippets to call these functions as appropriate, rather than
inlining the same code over and over.
(func_config, func_features, func_enable_tag, func_mode_help):
Factored out from the shared option parsing loop.  Write a new
shared option parser based on the one in libtoolize.in.
(func_check_version_match): Factored out from global scope.
(func_mode_compile, func_mode_execute, func_mode_finish)
(func_mode_install, func_mode_link, func_mode_uninstall): Break
each of the top level mode handlers out into a function.  Adjust
main loop.
(modename, prevopt, prev, optarg, show_help): Removed in the
course of cleaning up the shared option parser.
(opt_duplicate_deps): Use `:' and `false' instead of `yes' and `',
so we can run it directly, rather than calling test.