Pick some lowhanging fruit. (some memory leaks and unused variables)

Imported-from: https://svn.code.sf.net/p/dosbox/code-0/dosbox/trunk@4264

src/dos/dos_execute.cpp

@@ -315,6 +315,7 @@ bool DOS_Execute(char * name,PhysPt block_pt,Bit8u flags) {
 		envseg=block.exec.envseg;
 		if (!MakeEnv(name,&envseg)) {
 			DOS_CloseFile(fhandle);
+			delete [] loadbuf;
 			return false;
 		}
 		/* Get Memory */		

src/hardware/ipx.cpp

@@ -1072,7 +1072,7 @@ Bitu IPX_ESRHandler(void) {
 			CALLBACK_RunRealFar(RealSeg(ESRList->getESRAddr()),
 								RealOff(ESRList->getESRAddr()));
 		}
-		delete ESRList;
+		delete ESRList; //Destructor updates this pointer to the next value or NULL
 	}	// while
 
 	IO_WriteB(0xa0,0x63);	//EOI11

src/shell/shell.cpp

@@ -134,7 +134,10 @@ AutoexecObject::~AutoexecObject(){
 			if ((strncasecmp(buf2,"set ",4) == 0) && (strlen(buf2) > 4)){
 				char* after_set = buf2 + 4;//move to variable that is being set
 				char* test = strpbrk(after_set,"=");
-				if (!test) continue;
+				if (!test) {
+					delete [] buf2;
+					continue;
+				}
 				*test = 0;
 				stringset = true;
 				//If the shell is running/exists update the environment

src/shell/shell_misc.cpp

@@ -368,7 +368,7 @@ void DOS_Shell::InputCommand(char * line) {
 
 	// remove current command from history if it's there
 	if (current_hist) {
-		current_hist=false;
+		// current_hist=false;
 		l_history.pop_front();
 	}