http://www.bay12games.com/dwarves/mantisbt/view.php?id=1445

0x9461
90 90 90 90 90 90 90 90 90 90 90 90 90 90
C7 44 24 18 01 00 00 00 FF A0 44 01 00 00

.text:08051461 sub_8051461     proc near
.text:08051461                 mov     dword ptr [esp+18h], 1
.text:08051469                 jmp     dword ptr [eax+144h]
.text:08051469 sub_8051461     endp

0x9548
90 90 90 90 90 90 90 90
FF 4C 24 14 78 08 EB 0B

.text:08051548 loc_8051548:
.text:08051548                 dec     dword ptr [esp+14h]
.text:0805154C                 js      short loc_8051556
.text:0805154E                 jmp     short loc_805155B

0x9556
90 90 90 90 90 90 90 90 90 90
E9 F6 8C 05 00 E9 D0 8D 05 00

.text:08051556 loc_8051556:
.text:08051556                 jmp     loc_80AA251
.text:0805155B loc_805155B:
.text:0805155B                 jmp     loc_80AA330

0x9568
90 90 90 90 90 90 90 90
FF 4C 24 14 78 E8 EB 06

.text:08051568 loc_8051568:
.text:08051568                 dec     [esp+14h]
.text:0805156C                 js      short loc_8051556
.text:0805156E                 jmp     short loc_8051576

0x9576
90 90 90 90 90
E9 4D 8E 05 00

.text:08051576 loc_8051576:
.text:08051576                 jmp     loc_80AA3C8

0x62243
FF 90 44 01 00 00
E8 19 72 FA FF 90

<<<<
.text:080AA243                 call    dword ptr [eax+144h]
====
.text:080AA243                 call    sub_8051461
.text:080AA248                 nop
>>>>

0x62369
E9 E3 FE FF FF
E9 DA 71 FA FF

<<<<
.text:080AA369                 jmp     loc_80AA251
====
.text:080AA369                 jmp     loc_8051548
>>>>

0x623f6
E9 56 FE FF FF
E9 6D 71 FA FF

<<<<
.text:080AA3F6                 jmp     loc_80AA251
====
.text:080AA3F6                 jmp     loc_8051568
>>>>

basically:

+ int allowed_count = 1; // to mean 2
  ...
- if (type(item) == new_type)
+ if (type(item) == new_type && --allowed_count < 0)
    return false;

to allow up to two items of the same type at the same time

---8<---
This difference file is created by The Interactive Disassembler

Dwarf_Fortress
00009461: 90 C7
00009462: 90 44
00009463: 90 24
00009464: 90 18
00009465: 90 01
00009466: 90 00
00009467: 90 00
00009468: 90 00
00009469: 90 FF
0000946A: 90 A0
0000946B: 90 44
0000946C: 90 01
0000946D: 90 00
0000946E: 90 00
00009548: 90 FF
00009549: 90 4C
0000954A: 90 24
0000954B: 90 14
0000954C: 90 78
0000954D: 90 08
0000954E: 90 EB
0000954F: 90 0B
00009556: 90 E9
00009557: 90 F6
00009558: 90 8C
00009559: 90 05
0000955A: 90 00
0000955B: 90 E9
0000955C: 90 D0
0000955D: 90 8D
0000955E: 90 05
0000955F: 90 00
00009568: 90 FF
00009569: 90 4C
0000956A: 90 24
0000956B: 90 14
0000956C: 90 78
0000956D: 90 E8
0000956E: 90 EB
0000956F: 90 06
00009576: 90 E9
00009577: 90 4D
00009578: 90 8E
00009579: 90 05
0000957A: 90 00
00062243: FF E8
00062244: 90 19
00062245: 44 72
00062246: 01 FA
00062247: 00 FF
00062248: 00 90
0006236A: E3 DA
0006236B: FE 71
0006236C: FF FA
000623F7: 56 6D
000623F8: FE 71
000623F9: FF FA