It's sometimes useful to know whether there's been editing activity in a window. This PR adds that information to the ctl file. Change-Id: I21a342ac636dd5c7701b3ed560e3526867329c2c

Before, executing Get in a file rewound the window offset and selection to the start of the file. After this CL, Get preserves the window offset and selection, where preserve is defined as "the same line number and rune offset within the line". So if the window started at line 10 before and the selection was line 13 chars 5-7, then that will still be true after Get, provided the new content is large enough. This should help the common situation of plumbing a compiler error, realizing the window is out of date, clicking Get, and then losing the positioning from the plumb operation.

Bad remote file systems can change mtime unexpectedly, and then there is the problem that git rebase and similar operations like to change the files and then change them back, modifying the mtimes but not the content. Avoid spurious Put errors on both of those by checking file content. (False positive "modified since last read" make the real ones difficult to notice.)

If the mouse was in the tag of the old window, it was most likely pointing at Del. If bringing up a new window from below and not moving the mouse somewhere else, adjust it so that it ends up pointing at Del in the replacement window's tag too. This makes it easy to Del a sequence of windows in a column, from top to bottom. http://www.youtube.com/watch?v=ET8w6RT6u5M R=r http://codereview.appspot.com/6558047

See the comment in wind.c about why this isn't the right solution.

to an actual flag. buffer underrun check in number add xdata file for exactly the addressed region save addr across opens