age out: properly clean up lc_files linkage too

Summary: didn't catch this last night because I was focused mostly on
Linux.  On case insensitive filesystems we also need to clean up the
lc_files linkage to avoid a crash during age out.

The multiple attempts I added to the integration test trigger this
issue: `arc unit tests/integration/age.php`

Refs: #96

arcanist/lib/WatchmanInstance.php

@@ -238,6 +238,14 @@ function start() {
       throw new Exception("Failed to talk to watchman on $sockname");
     }
     stream_set_timeout($this->sock, self::TIMEOUT);
+
+    // If you're debugging and want to attach a debugger, then:
+    // `WATCHMAN_DEBUG_WAIT=1 arc unit tests/integration/age.php`
+    // then gdb -p or lldb -p with the PID it prints out
+    if (getenv("WATCHMAN_DEBUG_WAIT")) {
+      printf("PID: %d\n", $this->getProcessID());
+      sleep(10);
+    }
   }
 
   private function fwrite_all($sock, $buf) {

root.c

@@ -1416,6 +1416,17 @@ static void age_out_file(w_root_t *root, w_ht_t *aged_dir_names,
     // Remove the entry from the containing dir hash
     w_ht_del(file->parent->dirs, w_ht_ptr_val(full_name));
   }
+  if (file->parent->lc_files) {
+    // Remove the entry from the containing lower case files hash,
+    // but only it it matches us (it may point to a different file
+    // node with a differently-cased name)
+    w_string_t *lc_name = w_string_dup_lower(file->name);
+    if (w_ht_get(file->parent->lc_files, w_ht_ptr_val(lc_name))
+        == w_ht_ptr_val(file)) {
+      w_ht_del(file->parent->lc_files, w_ht_ptr_val(lc_name));
+    }
+    w_string_delref(lc_name);
+  }
 
   // resolve the dir of the same name and mark it for later removal
   // from our internal datastructures