Patch 7.0.084

Patch 7.0.084
Problem:    The garbage collector may do its work while some Lists or
           Dictionaries are used internally, e.g., by ":echo" that runs into
           the more-prompt or ":echo [garbagecollect()]".
Solution:   Only do garbage collection when waiting for a character at the
           toplevel.  Let garbagecollect() set a flag that is handled at the
           toplevel before waiting for a character.
Files:      src/eval.c, src/getchar.c, src/globals.h, src/main.c

git-svn-id: https://vim.svn.sourceforge.net/svnroot/vim/vim7@96 2a77ed30-b011-0410-a7ad-c7884a0aa172