libext2fs: don't inline ext2fs_open_file() and ext2fs_stat()

libext2fs: don't inline ext2fs_open_file() and ext2fs_stat()

The creation of inline wrappers ext2fs_open_file() and ext2fs_stat()
in commit c859cb1de0d624caa0779fb17d1a53766143136e in ext2fs.h caused
difficulties with the use of headers, since the headers for open64()
and stat64() may already be included (and skip the declaration of the
64-bit variants) before ext2fs.h is ever read.  There is no real way
to solve the missing prototypes and resulting compiler warnings inside
ext2fs.h.

Since ext2fs_open_file() and ext2fs_stat() are not performance
critical operations, they do not need to be inline functions at all,
and the needed function headers can be handled properly in one file.

Similarly, posix_memalloc() was having difficulties with headers, and
was being defined in ext2fs.h, but it is now only being used by a
single file, so move the required header there.

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>