Fix corner cases in AS_LITERAL_IF and AS_TR_SH.
* lib/m4sugar/m4sh.m4 (AS_LITERAL_IF): Fix bug with unbalanced
parens. Move guts...
(_AS_LITERAL_IF): into new helper.
(AS_TR_SH, AS_TR_CPP): Fix bugs with expansion of wrong macro.
Move guts...
(_AS_TR_SH, _AS_TR_SH_LITERAL, _AS_TR_SH_INDIR, _AS_TR_CPP)
(_AS_TR_CPP_LITERAL, _AS_TR_CPP_INDIR): ...into new helpers.
(AS_VAR_PUSHDEF): Hoist m4_require, by moving guts...
(_AS_VAR_PUSHDEF): ...into new helper.
* tests/m4sh.at (AS@&t@_LITERAL_IF): Enhance test.
Signed-off-by: Eric Blake <ebb9@byu.net>