Declare wait_screen_change earlier

[foursixnine]

When ::wait_screen_change it is translated internally to
&main::wait_screen_change which means that the symbol will be looked
into the current program instead of the proper library where the method
is defined

[rwx788]

#689

[rwx788]

LGTM

[rwx788]

Hmm, I wonder if your change could actually break all the tests (doubt that). Could you please restart them?

[foursixnine]

@rwx788 Actually it's my change that breaks all tests :) I guess a bit of reading is in order...
Quickly updating the prototype of the function results in:

Press ENTER or type command to continue
03-testapi.t .. Type of arg 1 to testapi::wait_screen_change must be block or sub {} (not array dereference) at ../testapi.pm line 604, near "@_) "
Bareword "is_serial_terminal" not allowed while "strict subs" in use at ../testapi.pm line 827.
Type of arg 1 to testapi::wait_screen_change must be block or sub {} (not reference constructor) at ../testapi.pm line 1214, near "};"
Bareword "is_serial_terminal" not allowed while "strict subs" in use at ../testapi.pm line 1265.
Type of arg 1 to testapi::wait_screen_change must be block or sub {} (not reference constructor) at ../testapi.pm line 1282, near "};"
Compilation failed in require at 03-testapi.t line 98.
BEGIN failed--compilation aborted at 03-testapi.t line 98.
03-testapi.t .. Dubious, test returned 255 (wstat 65280, 0xff00)
No subtests run 

[rwx788]

So it's even more broken =)))

[foursixnine]

Closing in favor of #1142