Rename length_cstring into size_cstring

The name size_cstring reflects that the returned
value is the number of bytes of the string.

This value may be not the same as the number of
characters contained in the string.
Implement genericcast_memblock

Allows to cast a pointer to a generic object with members
addr and size to type pointer to memblock_t.
Adapt Header Template to year 2013
Implement PRINTINT64_LOG

Macro prints a variable of type int64_t to the log.
Implement advisereadahead for file_t type

int advisereadahead_file(file_t fileobj, off_t offset, off_t length)
 * Expects data to be accessed sequentially and in the near future.
 * The operating system is advised to read ahead the data beginning at offse
 * right now. The value 0 for length means: until the end of the file.

int advisedontneed_file(file_t fileobj, off_t offset, off_t length)
 * Expects data not to be accessed in the near future.
 * The operating system is advised to free the page cache for the file begin
 * for length bytes. The value 0 for length means: until the end of the file
Use readahead in type instream_mmfile_t

The instream_t adapter (instream_mmfile_t) now advises
the operating system to read ahead a file opened for
read access.