I installed the version of LNet which is distributed by Online-Package-Manager (OPM) in Win10 64-bit (Laz 1.8.2 / 32 bit) and in Linux Mint 18.1 (32 bit) (Laz trunk / fpc 3.04) - and none of the installations made any problems.
And yes, I can confirm that the svn version does not compile with fpc 3.0.4 and below. If I switch to fpc-trunk, however, no problems here, too.
If you don't know OPM - it is coming with Lazarus since version 1.8, but it is not installed by default. Open "Packages" > "Install/Uninstall packages", find "OnlinePackageManager" in the right list of "available packages", click "Install selection" and "Save and rebuild IDE". After the installation has completed and Lazarus has restarted you'll find OPM in the menu "Packages" as last item.