Return -1 only on failure to execute a program.
Return -1 only on failure to execute a program.

Also fix some comments.

git-svn-id: a4a6f32337ebd29ad4763b423022f00f68d1c7b7@109499 91177308-0d34-0410-b5e6-96231b3b80d8

lodyagin/bare_cxx,lodyagin/bare_cxx,lodyagin/bare_cxx,lodyagin/bare_cxx,lodyagin/bare_cxx