Fixed problems with (new) environment variable for DLL source path.

src/sbbs3/ctrl/makelibs.bat

 @echo off
-set dllsrc ..\msvc.win32.dll.debug
+set dllsrc=..\msvc.win32.dll.debug
 implib -a sbbs.lib 	%dllsrc%\sbbs.dll
-implib -a mailsrvr.lib 	%dllsrc\mailsrvr.dll
-implib -a ftpsrvr.lib 	%dllsrc\ftpsrvr.dll
+implib -a mailsrvr.lib 	%dllsrc%\mailsrvr.dll
+implib -a ftpsrvr.lib 	%dllsrc%\ftpsrvr.dll