CFG path contraction condition was removing entry blocks

[macrologist]

Addresses #911

Path contraction in the CFG construction was allowing for entry blocks to be removed, despite declaring such behavior to be illegal in the comment preceding that removal.

[macrologist]

Compiling

DECLARE ro BIT
DECLARE shot_count INTEGER[1]

LABEL @START
SUB shot_count[0] 1
JUMP-UNLESS @END shot_count[0]
JUMP @START
LABEL @END

should emit something like

DECLARE ro BIT
DECLARE shot_count INTEGER

JUMP @START                             # Entering/exiting rewiring: (#(0 1 2 3 4 5 6 7) . #(0 1 2 3 4 5 6 7))
LABEL @END                              # Entering rewiring: #(0 1 2 3 4 5 6 7)
HALT                                    # Exiting rewiring: #(0 1 2 3 4 5 6 7)
LABEL @START                            # Entering rewiring: #(0 1 2 3 4 5 6 7)
MEASURE 0 ro[0]
SUB shot_count[0] 1
JUMP-WHEN @START shot_count[0]
JUMP @END                               # Exiting rewiring: #(0 1 2 3 4 5 6 7)

[macrologist]

bah hold on. RESETS are now generating a pointless jump-to-next-position sequence:

RESET

is becomming

JUMP @RESET-3323                       
LABEL @RESET-3323                       
RESET

working on it.

[macrologist]

Should be good. Tests pass on my Mac

[stylewarning]

Can we just add a couple tests for the previously failing cases?

[macrologist]

@stylewarning I added tests to cover the inciting example and one other