Added a more detailed error message on calling an ambiguous missing function.

mysql-test/r/ps.result:
  Bug #38159: fixed existing tests
mysql-test/r/sp-error.result:
  Bug #38159: test case
mysql-test/t/ps.test:
  Bug #38159: fixed existing tests
mysql-test/t/sp-error.test:
  Bug #38159: test case
sql/item_func.cc:
  Bug #38159: generate more detailed error message
sql/share/errmsg.txt:
  Bug #38159: add a more detailed error message
sql/sql_derived.cc:
  Bug #38159: treat the detailed error message the same way as the
  generic one
sql/sql_lex.cc:
  Bug #38159: 
    - detect if the token is ambiguous and print the appropriate error.
    - backport is_lex_native_function() from 5.1
sql/sql_lex.h:
  Bug #38159: detect if the token is ambiguous and print the appropriate error.
sql/sql_yacc.yy:
  Bug #38159: generate more detailed error message
sql/table.cc:
  Bug #38159: treat the detailed error message the same way as the
  generic one