bug on context

[zhanghuan]

hi all.

Here is a patch fixing a bug on MM error while returning to previous menu. 
The following steps should issue the bug:
1. write a menuentry using configfile command to load another menu file;
2. press 'ESC' to return to previous one;
3. repeat 1 and then repeat 2.

After looking into the code, I found that when a context is close, it frees all 
variables of the previous context instead of what it owned.



Zhang Huan
Tel: (86)10-6260-0549
Mailing: P. O. Box 2704# Beijing
Postcode: 100080
National Research Centre for High Performance Computers
Institute of Computing Technology, Chinese Academy of Sciences
No. 6, South Kexueyuan Road, Haidian District
Beijing, China

xxx.patch
Description: Binary data