Defines starting with `i' in src

• I_FULLSCRN src/doomdef.h:1044
• I_FULLVIEW src/doomdef.h:1041
• __I_HEADER_H__ src/i_header.h:2
• I_MESSAGES src/doomdef.h:1043
• INFRATICS src/doomdef.h:466
• INITSCALEMTOF src/am_map.h:79
• I_NOUPDATE src/doomdef.h:1040
• INVERSECOLORMAP src/r_local.h:31
• INVISTICS src/doomdef.h:465
• INVULNTICS src/doomdef.h:464
• IRONTICS src/doomdef.h:467
• I_STATBAR src/doomdef.h:1042
• ITEM_HEIGHT src/mn_menu.c:14