* (gdb.base/watch_thread_num.exp): Add breakpoint at thread_function
and record first explicitly generated thread number.
Use that thread number for thread specific watchpoint test.
Add iteration number to repetitive tests.
"thread" parameter to the watchpoint command and set the
"thread" member of the breakpoint struct.
* doc/gdb.texinfo: Add new parameter's description.
* testsuite/gdb.base/watch_thread_num.c: New testcase source file.
* testsuite/gdb.base/watch_thread_num.exp: New testcase expect file.