Make it easier to write deterministic tests.

Make it easier to write deterministic tests.

Continues Akim's work from his 2009-06-10 commits.
* src/reader.c (check_and_convert_grammar): Don't add any
symbols after the first symbols_do invocation.
* src/symtab.c (symbols_sorted): New static global.
(user_token_number_redeclaration): Update comments.
(symbol_from_uniqstr): If a new symbol is being created, assert
that symbols_sorted hasn't been allocated yet.
(symbols_free): Free symbols_sorted.
(symbols_cmp, symbols_cmp_qsort): New functions.
(symbols_do): Sort symbol_table into symbols_sorted on first
invocation.
* tests/input.at (Numbered tokens): Recombine tests now that the
output should be deterministic across multiple numbers.
(cherry picked from commit 83b60c97ee1f98bb1f15ffa38acdc4cc765515f5)