gitk: prevent overly long command lines

To avoid running into command line limitations, some of Git's commands
support the `--stdin` option.

Let's use exactly this option in the three rev-list/log invocations in
gitk that would otherwise possibly run the danger of trying to invoke a
too-long command line.

While it is easy to redirect either stdin or stdout in Tcl/Tk scripts,
what we need here is both. We need to capture the output, yet we also
need to pipe in the revs/files arguments via stdin (because stdin does
not have any limit, unlike the command line). To help this, we use the
neat Tcl feature where you can capture stdout and at the same time feed
a fixed string as stdin to the spawned process.

One non-obvious aspect about this change is that the `--stdin` option
allows to specify revs, the double-dash, and files, but *no* other
options such as `--not`. This is addressed by prefixing the "negative"
revs with `^` explicitly rather than relying on the `--not` option
(thanks for coming up with that idea, Max!).

This fixes #1987

Analysis-and-initial-patch-by: Max Kirillov <max@max630.net>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

gitk-git/gitk

@@ -540,14 +540,16 @@ proc start_rev_list {view} {
         if {$revs eq {}} {
             return 0
         }
-        set args [concat $vflags($view) $revs]
+        set args $vflags($view)
     } else {
+        set revs {}
         set args $vorigargs($view)
     }
 
     if {[catch {
         set fd [open [concat | git log --no-color -z --pretty=raw $show_notes \
-                        --parents --boundary $args "--" $files] r]
+                        --parents --boundary $args --stdin \
+                        "<<[join [concat $revs "--" $files] "\\n"]"] r]
     } err]} {
         error_popup "[mc "Error executing git log:"] $err"
         return 0
@@ -689,13 +691,19 @@ proc updatecommits {} {
             set revs $newrevs
             set vposids($view) [lsort -unique [concat $oldpos $vposids($view)]]
         }
-        set args [concat $vflags($view) $revs --not $oldpos]
+        set args $vflags($view)
+        foreach r $oldpos {
+                lappend revs "^$r"
+        }
     } else {
+        set revs {}
         set args $vorigargs($view)
     }
     if {[catch {
         set fd [open [concat | git log --no-color -z --pretty=raw $show_notes \
-                        --parents --boundary $args "--" $vfilelimit($view)] r]
+                        --parents --boundary $args --stdin \
+                        "<<[join [concat $revs "--" \
+                                $vfilelimit($view)] "\\n"]"] r]
     } err]} {
         error_popup "[mc "Error executing git log:"] $err"
         return
@@ -10366,10 +10374,16 @@ proc getallcommits {} {
             foreach id $seeds {
                 lappend ids "^$id"
             }
+            lappend ids "--"
         }
     }
     if {$ids ne {}} {
-        set fd [open [concat $cmd $ids] r]
+        if {$ids eq "--all"} {
+            set cmd [concat $cmd "--all"]
+        } else {
+            set cmd [concat $cmd --stdin "<<[join $ids "\\n"]"]
+        }
+        set fd [open $cmd r]
         fconfigure $fd -blocking 0
         incr allcommits
         nowbusy allcommits