Don't use broken BusyBox less as default pager.

Fixes #778

This is the flavor of less that ships by default in Alpine Linux. We're detecting it by checking whether `less` is a symlink that includes `busybox` in the path. There may be false negatives, but shouldn't be (m)any false positives?

This default can be overridden by explicitly setting less as the pager via PsySH config, if you really want to, but you probably don't. Install proper `less` instead :)

src/Configuration.php

@@ -1253,6 +1253,16 @@ public function getPager()
                 $this->pager = $pager;
             } elseif ($less = $this->configPaths->which('less')) {
                 // check for the presence of less...
+
+                // n.b. The busybox less implementation is a bit broken, so
+                // let's not use it by default.
+                //
+                // See https://github.com/bobthecow/psysh/issues/778
+                $link = @\readlink($less);
+                if ($link !== false && \strpos($link, 'busybox') !== false) {
+                    return false;
+                }
+
                 $this->pager = $less.' -R -F -X';
             }
         }