Low-memory behaviour fixes.

Fix unchecked buffer allocation in dbChannel.c
Replace calls to epicsStrDup() with checked malloc() for
things that happen often after iocInit.

Michael Davidsaver pointed out this issue.

src/ioc/db/dbChannel.c

@@ -465,6 +465,7 @@ dbChannel * dbChannelCreate(const char *name)
     const char *pname = name;
     DBENTRY dbEntry;
     dbChannel *chan = NULL;
+    char *cname;
     dbAddr *paddr;
     dbFldDes *pflddes;
     long status;
@@ -478,7 +479,14 @@ dbChannel * dbChannelCreate(const char *name)
         goto finish;
 
     chan = freeListCalloc(dbChannelFreeList);
-    chan->name = epicsStrDup(name);
+    if (!chan)
+        goto finish;
+    cname = malloc(strlen(name) + 1);
+    if (!cname)
+        goto finish;
+
+    strcpy(cname, name);
+    chan->name = cname;
     ellInit(&chan->filters);
     ellInit(&chan->pre_chain);
     ellInit(&chan->post_chain);

src/ioc/dbStatic/dbStaticLib.c

@@ -2113,7 +2113,9 @@ long dbPutString(DBENTRY *pdbentry,const char *pstring)
 		    return status;
 		}
                 /* store link text in case DTYP changes later */
-                plink->text = epicsStrDup(pstring);
+                plink->text = malloc(strlen(pstring) + 1);
+                if (plink->text)
+                    strcpy(plink->text, pstring);
 	    }
 	    if (strlen(pstring) >= sizeof(string)) {
 	        status = S_dbLib_badField;

src/libCom/iocsh/iocsh.cpp

@@ -284,11 +284,12 @@ cvtArg (const char *filename, int lineno, char *arg, iocshArgBuf *argBuf,
         break;
 
     case iocshArgPersistentString:
-        argBuf->sval = epicsStrDup(arg);
+        argBuf->sval = (char *) malloc(strlen(arg) + 1);
         if (argBuf->sval == NULL) {
             showError(filename, lineno, "Out of memory");
             return 0;
         }
+        strcpy(argBuf->sval, arg);
         break;
 
     case iocshArgPdbbase: