(petitioner cared for twin son of petitioner's half-brother as one of several persons that provided support for child, but did not substantiate amount of support; court determined that child not qualifying relative of petitioner (or anyone else) because petitioner could not establish provision of more than one-half of child's support; petitioner entitled, however, to dependency deduction because child qualifying child under I.R.C. Sec. 152(a)(1) by virtue of meeting tests contained in I.R.C. Sec. 152(c)(1)(B); on this point, court noted that IRS conceded that child met relationship test, satisfied age requirement and did not provide over one-half of own support; on issue of whether child shared same abode as petitioner, court noted that petitioner had stated on multiple occasions that child lived with petitioner for more than one-half of tax year, and discounted IRS arguments to the contrary).