Explicitly list cpp files for building wallet lib, fix Gitian build

[abitmore]

The Linux build was not reproducible due to the unstable ordering of source files for building the graphene_wallet library. This PR fixes it.

See bitshares/bitshares-gitian#38.

[abitmore]

Strange, Travis failed on push:

/home/travis/build/bitshares/bitshares-core/tests/tests/htlc_tests.cpp(787): error in "htlc_hardfork_test": check good_proposal_id(db).is_authorized_to_execute(db) failed

/home/travis/build/bitshares/bitshares-core/tests/tests/htlc_tests.cpp(807): error in "htlc_hardfork_test": check db.get_global_properties() .parameters.extensions.value.updatable_htlc_options->max_preimage_size == 2048u failed [19200 != 2048]

Will rerun.

Update: Travis passed on rerun.

Note: I found the htlc_hardfork_test test case does contain an issue, better clear trx before adding the proposal_update operation, but I don't think it caused the last failure.

bitshares-core/tests/tests/htlc_tests.cpp

Lines 784 to 787 in 06b0fe3

	trx.operations.push_back(uop);
	sign( trx, init_account_priv_key );
	db.push_transaction(trx);
	BOOST_CHECK(good_proposal_id(db).is_authorized_to_execute(db));