Fix possible memleak: defer putlog() from dns threads to main thread

[michaelortmann]

Found by: if it fixes #1545 then Mystery-X else michaelortmann
Patch by: michaelortmann
Fixes: could fix #1545

One-line summary:
Fix possible memory leak: defer debug() / putlog() from dns threads to main thread via dtn.strerror

Additional description (if needed):
valgrind doesnt like

Test cases demonstrating functionality (if applicable):
Test 1: 1 error in dnslookup leaks 144 bytes

$ valgrind --leak-check=full ./eggdrop -t BotA.conf
.tcl dnslookup foo bar
.die
==619111== 144 (16 direct, 128 indirect) bytes in 1 blocks are definitely lost in loss record 375 of 543
==619111==    at 0x4843788: malloc (vg_replace_malloc.c:442)
==619111==    by 0x49A36DA: TSDTableCreate (tclThreadStorage.c:88)
==619111==    by 0x49A36DA: TclThreadStorageKeySet (tclThreadStorage.c:230)
==619111==    by 0x49A25DC: Tcl_GetThreadData (tclThread.c:92)
==619111==    by 0x4981DE3: TclFreeObj (tclObj.c:1444)
==619111==    by 0x49B1DD4: CleanupVar (tclVar.c:344)
==619111==    by 0x49B1DD4: TclPtrUnsetVarIdx (tclVar.c:2513)
==619111==    by 0x49B49E8: TclObjUnsetVar2 (tclVar.c:2386)
==619111==    by 0x49B4B16: Tcl_UnsetVar2 (tclVar.c:2338)
==619111==    by 0x153CF7: check_tcl_bind (tclhash.c:955)
==619111==    by 0x154F25: check_tcl_log (tclhash.c:1252)
==619111==    by 0x143998: putlog (misc.c:563)
==619111==    by 0x13A158: thread_dns_ipbyhost (dns.c:560)
==619111==    by 0x51ED559: start_thread (pthread_create.c:447)

Test 2: 2 errors in (2) dnslookup leaks 288 bytes, so its scaling ouch

$ valgrind --leak-check=full ./eggdrop -t BotA.conf
.tcl dnslookup foo bar
.tcl dnslookup foo bar
.die
==658361== 288 (32 direct, 256 indirect) bytes in 2 blocks are definitely lost in loss record 402 of 543
==658361==    at 0x4843788: malloc (vg_replace_malloc.c:442)
==658361==    by 0x49A36DA: TSDTableCreate (tclThreadStorage.c:88)
==658361==    by 0x49A36DA: TclThreadStorageKeySet (tclThreadStorage.c:230)
==658361==    by 0x49A25DC: Tcl_GetThreadData (tclThread.c:92)
==658361==    by 0x4981DE3: TclFreeObj (tclObj.c:1444)
==658361==    by 0x49B1DD4: CleanupVar (tclVar.c:344)
==658361==    by 0x49B1DD4: TclPtrUnsetVarIdx (tclVar.c:2513)
==658361==    by 0x49B49E8: TclObjUnsetVar2 (tclVar.c:2386)
==658361==    by 0x49B4B16: Tcl_UnsetVar2 (tclVar.c:2338)
==658361==    by 0x153CF7: check_tcl_bind (tclhash.c:955)
==658361==    by 0x154F25: check_tcl_log (tclhash.c:1252)
==658361==    by 0x143998: putlog (misc.c:563)
==658361==    by 0x13A158: thread_dns_ipbyhost (dns.c:560)
==658361==    by 0x51ED559: start_thread (pthread_create.c:447)

gccs LeakSanitizer also finds it, but valgrinds report is more detailed