chgserver: more explicit about sensitive environ variables Environment variables like HGUSER, HGEDITOR, HGEDITFROM should not trigger a new chgserver. This patch uses a whitelist for environ variables starting with "HG" to reduce the number of servers. I have went through `grep -o "[\"']HG[A-Z_0-9]*['\"]" -hR . | sort -u` so the list should be up-to-date.

scmutil: make simplekeyvaluefile able to have a non-key-value first line To ease migration from files with version numbers in their first lines, we want simplekeyvaluefile to support a non-key-value first line. In this way, old versions of Mercurial will read such files, discover a newer version than the one they know how to handle and fail gracefully, rather than with exception. Shelve's shelvestate file is an example.