Typedefs starting with `t' in djgppdoom

• texpatch_t src/r_data.c:108
• texture_t src/r_data.c:126
• thinkerclass_t src/p_saveg.c:226
• thinker_t src/d_think.h:71
• think_t src/d_think.h:61
• tSigSet src/i_soorig:903