mem/resource leak fixes for trunk

Hi, I've been running reactos through a static analysis tool called Cppcheck and have discovered some memory and resource leaks throughout the code

Please find the attached patch on this report, review changes (in brackets) if necessary

The changes:

base/applications/downloader/xml.c:

• Missing fclose() on pointer after failure

base/services/dhcp/memory.c:

• Perform free() on pointer if not NULL, only if the other ||'s make it enter the code block

boot/freeldr/tools/deptool.c:

• Perform free()'s on pointers if not NULL, only if the other ||'s make it enter the code block
• free() pointers upon error conditions
• free() pointers at end of function

tools/buildno/buildno.cpp:

• Add condition when a memory allocation fails, fclose() and free() needed pointers and return;
• Add missing free() on error condition
• free() pointer at end of code block

tools/cdmake/cdmake.c:

• fclose() pointer on condition
• Remove double free (PLEASE CHECK)

tools/mkconfig.c:

• free() buffer on error condition before exiting
• free() buffer at end of function

tools/rbuild/rbuild.h:

• Derived class Include requires virtual destructor from classes ToolsetDirective, CompilerDirective

tools/rsym/log2lines.c:

• Add missing fclose()

tools/stubgen.c:

• Release resources before returning
• Use pclose() instead of fclose() on popen()'d pointer

Please make sure the changes are ok before committing, or fix if necessary