Fix sp-kill-hybrid-sexp bug in REPL-like modes

After killing a full line (i.e. sp-point-in-blank-line returns non-nil),
sp-kill-hybrid-sexp inserts a number of spaces equal to the value
of (current-column) before the kill was performed. When killing a full
line in a mode where the editable line begins at a non-zero column this
causes extraneous spaces to be inserted.

Instead, only insert the spaces (if any) necessary to get point back to
the original indentation level recorded before the kill.
Merge pull request #352 from johnmastro/fix-sp-kill-hybrid-sexp

Fix sp-kill-hybrid-sexp bug in REPL-like modes