lib/sh/util.sh: echo_func(): get call context before wrapper(s), which is more useful for debugging. this uses skip_stack_frames()'s lookahead=1 mode.

fix: lib/sh/util.sh: skip_stack_frames() callers: updated for new skip_stack_frames rather than get_stack_frame behavior

lib/sh/util.sh: skip_stack_frames(): added lookahead support, which looks at entry after current to deterine whether to skip current. this is useful for skipping wrappers, by looking at the calling function's name.

fix: lib/sh/util.sh: skip_stack_frames(): for new skip_stack_frames rather than get_stack_frame behavior, stack frames must be skipped in the caller to preserve the stack frame pointer

lib/sh/util.sh: get_stack_frame_after(): renamed to skip_stack_frames() for clarity

lib/sh/util.sh: added skip_stack_frame_in_caller, unskip_stack_frame_in_caller

lib/sh/util.sh: added prev_stack_frame

lib/sh/util.sh: echo_func(): use new format_stack_frame, which adds call context information to what was provided by func_loc

fix: lib/sh/util.sh: format_stack_frame(): need to hide canon_rel_path() info using log+

lib/sh/util.sh: added get_stack_frame_after()