memory leak on proj objects when using proj's threadsafe api

[tbonfort]

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==23873== 520 (328 direct, 192 indirect) bytes in 1 blocks are definitely lost in loss record 37 of 45
==23873==    at 0x4C28BED: malloc (vg_replace_malloc.c:263)
==23873==    by 0x52E08A7: pj_malloc (pj_malloc.c:19)
==23873==    by 0x52DBD39: pj_longlat (pj_latlong.c:61)
==23873==    by 0x52DFBBB: pj_init_ctx (pj_init.c:280)
==23873==    by 0x4F2F81A: msProcessProjection (mapfile.c:1218)
==23873==    by 0x4F2FBDE: msLoadProjectionStringEPSG (mapfile.c:1352)
==23873==    by 0x4F88CEF: msWMSLoadGetMapParams (mapwms.c:1133)
==23873==    by 0x4F9730F: msWMSDispatch (mapwms.c:4859)
==23873==    by 0x4FCA2BF: msOWSDispatch (mapows.c:243)
==23873==    by 0x5037292: msCGIDispatchRequest (mapservutil.c:1631)
==23873==    by 0x401654: main (mapserv.c:257)
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