Fix all compiling errors

Signed-off-by: Hongjiu Zhang <zhanghj@umich.edu>
Fix a lot of segfault errors

Signed-off-by: Hongjiu Zhang <zhanghj@umich.edu>
Fix all segmentation fault errors.

Signed-off-by: Hongjiu Zhang <zhanghj@umich.edu>
Change VarDecl to errorType to avoid cascading error
Fix more errors

  * Makefile: Add full debugging information.
  * ast_decl.cc, ast_decl.h: Add InterfaceDecl::GetMemberFn and
    InterfaceDecl::GetFn.
  * ast_expr.cc: Fix the type of EqualityExpr. Fix the type checking of
    ArrayAccess.

Signed-off-by: Hongjiu Zhang <zhanghj@umich.edu>
Fix bug in FieldAccess
Fix bugs in FieldAccess
Fix a stupid error in ArrayType::DoCheck()

  * ast_type.cc(ArrayType::DoCheck): Fix an improper condition.

Signed-off-by: Hongjiu Zhang <zhanghj@umich.edu>
Fix error report for NumArgsMismatch

  * ast_decl.cc, ast_decl.h: Add a new argument for caller.
  * ast_expr.cc: Fix the call arguments for the new formals.

Signed-off-by: Hongjiu Zhang <zhanghj@umich.edu>
Fix the type checking of RelationalExpr
  * ast_expr.cc(RelationalExpr::DoCheck): Always return Type::boolType.

Signed-off-by: Hongjiu Zhang <zhanghj@umich.edu>
Fix checking private access inside a class

  * ast_expr.cc: Accept accessing a private field inside a class.

Signed-off-by: Hongjiu Zhang <zhanghj@umich.edu>
Add length Class
Fix bugs about interface