Make define-package macro expansion more backwards compatible

Only include `:local-nicknames` as an argument to `ensure-package` if it is
non-NIL.

Fixes #84
17 jobs for !189 with iss84-define-package in 67 minutes and 43 seconds (queued for 5 seconds)
Child pipeline (parent) latest detached
Status Name Job ID Coverage
  Build
passed Build ASDF #17610

00:02:26

passed Build docs #17611

00:08:36

 
  Regression
failed Regression test expected failure: [abcl, latest] #17619
allowed to fail

00:37:31

passed Regression test: [abcl, 1.7.1-jdk8] #17618

00:42:16

passed Regression test: [ccl, latest] #17612

00:12:27

passed Regression test: [clasp, latest] #17613

00:39:01

passed Regression test: [clisp, latest] #17614

00:07:28

passed Regression test: [cmucl, latest] #17615

00:07:38

passed Regression test: [ecl, latest] #17616

00:07:31

passed Regression test: [sbcl, latest] #17617

00:05:33

 
  Upgrade
passed REQUIRE upgrade test: [abcl, latest] #17620

00:06:51

passed REQUIRE upgrade test: [ccl, latest] #17621

00:01:17

passed REQUIRE upgrade test: [clasp, latest] #17622

00:09:50

passed REQUIRE upgrade test: [clisp, latest] #17623

00:01:31

passed REQUIRE upgrade test: [cmucl, latest] #17624

00:01:34

passed REQUIRE upgrade test: [ecl, latest] #17625

00:04:02

passed REQUIRE upgrade test: [sbcl, latest] #17626

00:01:22

 
Name Stage Failure
failed
Regression test expected failure: [abcl, latest] Regression
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