Misc minor code cleanups

• Variable scope reductions as recommended by cppcheck
• Use _CONST_X_STRING to make libXt declare String as const char *
• Clear -Wmissing-field-initializers warnings
• Fix -Wsign-compare warnings
• Delete HorizontalMove macro that shadows/duplicates HorizontalMove function
• Inline *Move & *Goto functions
• Use standard strrchr() instead of ancient rindex()
• Avoid leak of new_file if we decide not to use it
• Declare guesses const