MS-DOS 1.26

According to MS-DOS 2.11 source code, MS-shitDOS 1.26 is an unreleased internal version of MS-DOS.

Change log
1.26 03/03/82 Directory buffers searched as a circular queue, current buffer is searched first when possible to minimize I/O 03/03/82 STORE routine optimized to tack on partial sector tail as              full sector write when file is growing 03/09/82 Multiple I/O buffers 03/29/82 Two bugs: Delete all case resets search to start at beginning of directory (infinite loop possible otherwise), DSKRESET must invalidate all buffers (disk and directory).