Merge remote-tracking branch 'origin/vm/page-swap-synch' into vm/virtual-memory/saleh

# Conflicts:
#	.gitlab-ci.yml
#	src/Makefile.build
#	src/threads/thread.c
#	src/userprog/exception.c
#	src/userprog/process.c
#	src/vm/frame.c
#	src/vm/page.c
#	src/vm/page.h
#	src/vm/stackgrowth.c
#	src/vm/stackgrowth.h

src/threads/thread.h

@@ -149,6 +149,10 @@ struct thread
     struct hash open_files;             /* Hash Table of FD -> Struct File. */
 #endif
 
+#ifdef VM
+  struct hash pages;                    /* Table of open user pages. */
+#endif
+
     void *curr_esp;
 
     /* Owned by thread.c. */