vi: install SIGINT handler _after_ restart setjmp is initialized

vi: install SIGINT handler _after_ restart setjmp is initialized

While at it, sanitized comment style, deleted wrong ones, renamed signal
handlers to <sig>_handler(), slightly optimized "cursor home+clear screen".

function                                             old     new   delta
cont_handler                                           -      66     +66
tstp_handler                                           -      64     +64
winch_handler                                          -      60     +60
int_handler                                            -      32     +32
edit_file                                            648     651      +3
redraw                                                52      43      -9
catch_sig                                             32       -     -32
winch_sig                                             60       -     -60
suspend_sig                                           64       -     -64
cont_sig                                              66       -     -66
------------------------------------------------------------------------------
(add/remove: 4/4 grow/shrink: 1/1 up/down: 225/-231)           Total: -6 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>