Allow for extra whitespace (such as \r) before end-of-line in certificates

Because we must decode the PEM format to DER before feeding to
Crypt::X509, we apply a regular expression to extract PEM data.
However, the regex must account for, and accept, \r\n-style newlines
which may arise from pasting content into the "SMIME Certificate" admin
interface.
Merge branch '4.2/smime-certificate-newlines' into 4.2.0-releng