DOC: Make API documentation for copy_ptree() visible to Doxygen
Correct misprint in error message of localfixpoint_goalmode()
BUGFIX: concerning lost edges among reached nodes in local-mu patching

In the method provided by patch_localfixpoint(), when pruning extra
edges during appending ("patching") of local strategy automata into
original, sometimes edges between nodes that are reached by the
solution of the reachability game were incorrectly deleted.

The erroneous behavior corrected by this commit is demonstrated by
applying the edge change file tests/specs/patching/gridworld_2x20_1obs.edc
to the specification tests/specs/patching/gridworld_2x20_1obs.spc

Also in this changeset, the first parameter of forward_modereach()
has been removed because it was not used.
With -vv, print DOT rendering of local_strategy in localfixpoint_goalmode()
Change txt output format to print state as comma-separated values

The "txt" output format, e.g., as it is called in the -t switch from
the command-line, is provided by list_aut_dump().