Fixes the cornercases:
beta.logpdf(0,1,0.5) == -0.69314718056
beta.logpdf(0,0.5,1) ==    inf
gamma._logpdf(0,1) == 0
Added comment to test.
Remove duplicate test
Merge branch 'master' of https://github.com/scipy/scipy into ticket1326_logpdf_fails_for_beta_and_gamma
Simplified code with calls to special.xlogy and special.xlog1py
beta._pdf now calls beta._logpdf
BUG: stats: make beta and betaprime pdfs work for a larger parameter range
Merge pull request #467 from pbrod/ticket1326_logpdf_fails_for_beta_and_gamma

BUG: stats: fix corner cases in beta, gamma, betaprime logpdfs